I don't think this would work because this scammers also changed passphrase function that is not working correctly in this altered Trezor devices, so you would only have false sense of better security.
Not to mention that using very long passphrase (on normal trezor device) is a bad idea, because you would have to enter this long passphrase every time for each transaction you make

That's a very good practice, and you're absolutely right that it would protect you against this 'fake passphrase' attack.
However it's still possible that the base seed is created from bad known entropy; that's something your method wouldn't spot. Though it wouldn't impact the entropy of your passphrase.

In general, I believe people put too much trust in passphrases. Every so often, when something's brought up like a hardware wallet having a bad source of entropy or not having a secure element, I hear something like 'Oh, just slap a passphrase on it' as a universal solution for all problems. If you were to put all your trust on the passphrase and expect the same entropy as the seed phrase itself, it would need to be much longer than what most people normally choose and can reliably remember.

I don't think you can XOR the seed checksums together without corrupting it, because the checksum function is not commutative.

Maybe Trezor is not using a checksum at the end of the 24 words and that's why it works well for you.

I can't even imagine typing all this ''strong long passphrase'' with special characters on hardware wallets like ledger or trezor model T, and you have to do this on devices only.
Since there are no wrong passphrases, a single mistake you make while typing would create new blank wallet with zero balance each time 
This would be nominated as most frustrating hardware wallet for sure.

But example you gave us before had multiple special characters and I wouldn't say this was balance between security and convenience

Well, it depends. Even a long and complex passphrase like the one witcher_sense posted I could enter in no more than 5 minutes. Sure, that's no use for a "daily spending" wallet, but if that's my cold storage wallet and I'm only accessing it wallet once or twice a year, then that is a perfectly acceptable balance of security and convenience.

In addition to Cricktor's reply above, if you are already using Ian Coleman safely on an airgapped computer, then it is trivial to use it to also calculate the correct checksum for your resulting XORed entropy.

Another day and another hack, this time for Trezor model T hardware wallet, and it was done by Crypto Security Firm Unciphered.
First thing I will say is that it's very strange coincidence for this news to be released in same time when ledger messed up with their Recover disaster news, but whatever.
 
I am not surprised at all about this, we all know that Trezor devices don't have secure element and if it was possible to do this with Trezor One than it was going to happen to Trezor Model T as well.
Maybe this was sponsored by one French company, or Unciphered simply decided to use this opportunity for their own promotion.

Unciphered build a custom board, connected Trezor T to it and they had to wait a long time for extraction of PIN and mneomonic words, but they eventually did it.



This is nothing new for all devices without secure element, but there are few ways people can protect against attacks like this:

1. Use multiple strong passphrases - this is easy and free solution available to anyone, and it makes hackers job much harder.
2. Use Multisig setup with your Trezor wallet - this makes it impossible for anyone to extract keys with this procedure.
3. Use Secret Shamir Sharing with passphrase - this should in theory work in similar way like Mutlisig setup.
4. Don't keep any of your keys inside wallet if you don't use it daily, only import when you need to send transaction and then reset it.
5. Use other open source hardware wallet with secure element.

Trezor is making their own secure element so new generation device will be much better, but knowing all this I was not recommending Trezor wallets for some time.
However, risk of this happening to regular people is very low, especially if you improve security like I mentioned.

Hacking Trezor T video process:
https://www.youtube.com/watch?v=50eiA-75NMY

It's no secret that both Trezor hardware wallets are vulnerable to physical manipulation and it was confirmed with several hacking videos in the past. This is somewhat similar to Joe Grand's video, which involves taking the device apart and doing some soldering and pins connecting work to a custom board. The hack itself uses different software and hardware.

What they didn't mention in the video is if the success rate depends on the firmware version of the Model T, or if it's equally easy/difficult to obtain the PIN and seed regardless of the firmware.

Ledger? I didn't get the feeling that zasad@ was trying to defend Ledger in any way. Maybe I misunderstood what you wanted to say.
 
Actually, Trezor's seed and PIN extraction vulnerabilities can't be fixed and require a complete overhaul of their devices. No firmware upgrades will ever fix Trezor One and Trezor T. The security researcher's in the video mentioned that as well.   

My gut feeling tells me he is trying to break a hardware wallet with a secure element chip. The future will show if he is successful with it or not. He will obviously never release any information until he has gotten in touch with the responsible parties and given them time to fix the problems. This is all assuming that he was successful in recovering sensitive information. 

strong passphrase solves the hacking problem if hackers manage to get to your Seed.
I am by no means justifying Trezor, but there are no ideal hardware wallets, and you have to adapt to those wallets that are on the market.

There is something else that worries me about Trezor. I was one of the first to order my Trezor T in 2018.
Then they sent it to me with a faulty USB cable, which upset me a little. A friend of mine also ordered a Trezor T two weeks ago and was also sent a wallet with a faulty cable.
It's been five years and Trezor hasn't been able to fix the problem with the USB cables. It's really a shame.