However for the end user it might create certain complications under specific circumstances.
Imagine Alice accumulated some amount of coins from her signature address on this forum.
She then decided to make a few payments and go to the party, so she sent a few transactions all from the same address in a short amount of time: one to bitmit, one to her friend and one to her mother she promised long time ago, then she shut down her computer and went partying.
Now with these rules in place (considering 1 tx from 1 address per block) her last two transactions were lost and she wouldn't figure this out until after she starts her computer again to re-broadcast them, which might take a few days or until her mother calls and asks where is the money

Yep. But thats why the actual tx/mempool is variable. I think 1 is probably too low for the reason you point out here. But I dont see many people needing more than 2-3 at maximum for any given use-case. A sane default, IMHO, would probably be around 3.
I'm still concerned this will have more impact on legitimate users or small businesses who process their transactions manually than on high volume makers.
New rules do not discourage the volume itself but using the same address in that volume.
So the change seems to be targeted to the current implementation of SatoshiDice rather than being a more generic solution.
Under new rules SatoshiDice will have to change that's for sure and there are two ways:
1) use sendmulti which is benevolent
2) use new addresses for each bet which is basically bypassing the new rule.
They have already admitted that they want to be a good citizens and they will put efforts to implement sendmulti, so introducing new rules just for them (or rather against them) doesn't make much sense. On the other hand players which choose to be malevolent will simply bypass the new rule by using new addresses if they wish to.
So is it really worth the time and effort, which otherwise could be spent on thinking about proper pruning solutions?