IMHO, the absolutely FIRST thing to do is to know (and increase) your personal limits for such cashing out. Of course, you can drizzle it out, but in situations like Dec 2017, you can "lose" 40% of the gains (or at least would not be able to re-deploy after withdrawal) if you cannot withdraw what you want to withdraw.
High(er) limits are certainly very handy.
Regarding the ability to remove value from various exchanges, surely there has been problems with both withdrawal limits and even surprise KYC (sometimes referred to as shotgun KYC) in the past, and sometimes people do not even know that they have withdrawal issues (or limitations) or even that new limitations are being put into place until they take actual steps towards withdrawing (presumptively large amounts - or maybe larger amounts than they had previously withdrawn - or even amounts that had not been purchased at that particular exchange).
So, surely could be a problem to ONLY have one way of withdrawing value from an exchange - whether withdrawing the dollar value or even the BTC value if and when such a time to withdraw were to come.
Your post, Biodom, reminded me of another idea, too.
I am not really opposed to the idea of a thought out plan that even increases the percentage of BTC that would be sold as the BTC price goes up (under the presumption that the BTC might be going up).
Surely, it becomes a bit more problematic to presume the next steps after selling the BTC as the price goes up - that the BTC price might go down - but of course, plan outlines can be made to figure out BTC price buyback points in the event that BTC prices were to go back down.. some people might be o.k. starting to buy back in small increments (such as 10% price drops), and other people might prefer larger price drops before buying back, such as waiting for 30% or more or even waiting for 50% or more before they would buy back. Those kinds of buy back thresholds could be predetermined (even while maintaining a competing idea in mind that such buy back thresholds might not be reached which will cause any buy back, NOT to happen) and then the buy back thresholds could be later tweaked, too.
Part of my presumption for any amount of BTC that is sold is that the HODLer who sells should be ready, willing and able to consider that act of selling his/her BTC as a complete exit out of BTC for the amount that was sold - of course, if subsequent events happen that allow for a rebuying, then so be it, but the underlying presumption that I like to keep in mind when selling BTC is to NOT be selling any such BTC and expecting to buy back lower - because the lower part of such idea might not happen.. In other words, such seller needs to be committed to the sale and willing to live with NOT being able to buy back at lower prices.