Remathilis
Legend
The obvious solution is to give warlocks a recharge mechanic, usable (proficiency bonus) times per day, which takes one minute. This would be consistent with the general thrust of 1D&D in moving short-rest mechanics to prof/day, and it solves the whole problem very neatly and cleanly.
That's not theorycrafting, by the way. My table has been using a house rule along those lines for years (a short rest is 5 minutes, capped at 2 per day per character) and it works great. Others on ENWorld have done the same.
As far as spell prep being based on spell slots... well, yeah, that's not going to work with pact magic. But that's only a problem if 1D&D insists on trying to modify pact magic to be more like other kinds of spellcasting, which is exactly what I'm arguing against.
So what, in practical terms, is the difference between giving a warlock 2 spell slots and 2 recharges and giving them 6 spell slots per day? I guess you can't go Nova in one fight, but assuming they aren't going for 5 minutes workday, the math is the same.
But I think the writing is on the wall if the bard is any indication. They were spontaneous casters with an eclectic mix of spells and now they use the same mechanics as all the other casters we've seen. I just don't see how WotC justifies the changes to bards or druids but then let's warlocks have a spell system that runs contrary to every other caster in the PHB.
I guess we'll find out in a packet or two.