There's a certain pattern I notice some of my players get into frequently that makes me worry about them getting bored and disengaging from the game. It goes something like this:
Me: "It's your turn"
Player: "I walk up and attack"
Me: "Do you have any bonus actions or resources to spend?"
Player: "Yes but I don't want to spend them, I might need them later"
Repeat for 10 turns, for several combats, and then a long rest happens.
I have seen this happen in D&D off and on since 95.
most resent I have played in a homebrew game as a warlock and HAD the fear for the first 5ish levels that I needed to hold my slots for BIG BOOM ENCOUNTERS... even though we were getting short rests.
I not only got around it in my head, but we had a multi class barbarian that had the opposite issue... he would at low level rage 1st 2 fights then complain something wasn't working... around the time I started not caring and using my slots he started to hoard his rages.
to the point that we had a day somewhere around 9thish level that we had taken multi short rests, I had used all my slots every time... and we had like 10ish encounters, and when we took the long rest he still had all of his rages.
I ALSO see it (both as a DM and player) with non renewable resources a lot.... "We should use our healing spells and wands and stuff before drinking potions" that leads to 13th level PCs in the end game having 3+ potions of healing that do 2d4+2 and saying "these don't seem worth it now"... yeah, cause you should have used them 8 levels ago.
This doesn't happen with every group, but for those that do this it makes combat feel uninteresting and downright anemic. I
yup... I miss the 4e encounter power concept... however I also remember "Everyone felt they were still doing the same thing every fight" I almost wish we had MORE type of recharge. "This power/ability/spell comes back every fight, this one takes a short rest, this one takes 4 hours rest or no, this one comes back on a long rest, and this one only recharges weekly or monthly." but I fear that is too complex.
A messy hypothetical implementation:
-Spell slots still return after a Long Rest, Pact Spell slots still return after Short Rests
-Non-spell slot Long Rest resources return after a Short Rest now
-Short rest resources relevant to combat return at the end of combat
-Short rest resources not relevant to combat remain as they are
-Enemies receive some kind of universal buff, like bonus damage on hit, to even the playing field and force more liberal use of abilities.
some classes get "if you don't have any of X when you start a fight regain Y number" at levels and I think that could work.