I've made substantial improvements following a couple of mocked and one live playtest. My ToA campaign group (6 players) preferred these rules to what we were using (a version of Gritty Realism). They found a defensible room and cycled through sleeps and meditations until everyone had taken a rest of the type they needed.
32 hours in all. The party started with a breather and dumped healing magic, reinforcing a belief that regaining full HP from rests is unnecessary. As expected, characters taking long meditation also chose to sleep afterwards.
Random Encounters
An encounter came up during the rest (I make a check per 8 hours). Three characters were
unconscious, and we found using that condition (which is articulated in the XGE sleep rules) worked neatly. The
unconscious characters felt appropriately vulnerable, and the active characters worked together to block tomb guardians from reaching them. Our rogue seemed pleased to find that with a 4-hour trance he was good to go. As DM, I loved that there was no doubt who was meditating and who was doing some kind of borderline activity: you're
unconscious.
Magic Items
Doubts came up about magic item charge refreshes. For now I am ruling that attuned items recharge with short and long meditation rather than sun cycles. As an example, a
staff of striking recharges d3 after short meditation and then 2d3+1 more after long. Seeing as short flows into long this is 3d3+1 or 1 better than repeated short meditations.
Suspension of Disbelief
I hoped that players would accept meditation as a fact about the world, and so far that seems to be working. They appear to appreciate that it was in some sense the ability to meditate that separated out "adepts" (aka PCs and generally, creatures with character-class equivalence). Attaching item attunement to sleep seems to help this.
Further Playtests
Going forward we'll learn what happens as rests are iterated. There are no mandatory cooldowns, so I am curious to discover if players will alpha and then meditate, or if the conditions are strict enough that they will prefer to run a good number of encounters. I'd also like to see if they ever short mediate without also pausing for long meditation, seeing as we have a monk, a battle master, a cleric and a bard. I'll post again after a few more game sessions.