You don't need to do anything if you don't want to. Your coins are totally safe in whatever version of Core that you're currently running.

Edit - And migrating to BU is pointless atm, consensus is a million miles away.

User node count could be used as another indication of user consensus, but I don't see where Bitcoin Unlimited is listed as a wallet at bitcoin.org, so it might not be the most reliable indicator.

I am assuming that the blockchain/wallet directory structure is the same, is this correct?
Is the official website https://www.bitcoinunlimited.info ?

I probably know how to go about it, but some might want step by step instructions. And of course I want to make sure I am not missing something.

I could downgrade to core 0.12.x and play with -maxmempool, -mempoolexpiry and -minrelaytxfee parameters.

You'll have to look at both Core and Unlimited and decide for yourself which provides the features you prefer.

At the protocol lvel, they are currently compatible with each other, so it doesn't matter much which you run.  If protocol changes activate and you change your mind, it isn't difficult to switch.

I can't pick and choose individual features so would have to decide on overall features. Think I might have read core 0.14 saves mempool data between restarts which is probably a very good idea.

Could I install both, and either fire one version up or the other over the same blockchain/wallet directory structure though? Or could that very well change before any consensus is achieved?

first of all
1. get the privkeys/seed and copy them. i dont mean just copy and paste the wallet.dat i mean ensure you have it copied down in other formats too and also copy the wallet.dat to a couple different locations/media devices (incase one or more gets corrupt)

2. then update

I maintain a bitcoin-core RPM that links against LibreSSL on CentOS 7.

I'm sorely tempted to rebuild 14 with a 2 MB block and undo the fee increase, just so people who use my build won't be hurt by what core developers are doing, and so clients will work when blocks > 1 MB come out.

I'm also tempted to just not build 0.14.x at all and only offer BU.

Why don't you wait for an agreement to be reached as to the future direction of Bitcoin before you make a move? If I were you I wouldn't rush to BU yet but will still run my Bitcoin core until a decision is made.

Trying to find an idiots guide to safely migrating from bitcoin core to bitcoin unlimited. I like the fact that my private keys are encrypted, so I need to be extremely careful with them if I have to dump them in native format to migrate.

It should be as easy as Danny describes, but it would be great to have a better write up that includes screenshots.  If you're using Windows or Mac (not Linux) and if you're interested in earning a bounty while you migrate, take screen shots and document the process that you went through, and then write a brief "idiots guide to safely migrating from Bitcoin Core to Bitcoin Unlimited" and post as a new thread here or on Medium, and I can send you $100 - $150 from our outreach fund (actual amount will depend on the quality of the finished product and be at my discretion).  

I may take you up on that.