I would love to hear you expand these thoughts a little more.
As a potentially related point: could you imagine if the game released with a much smaller catalog of spells in the PHB, but then the DMG had a list of spells that characters could discover through gameplay and also not just a wizard thing? Or even had it so that spells that were level 6+ had to be discovered? I sometimes think about that.
Real briefly, in my current Ravenloft game, the characters are all level 1, but don't have a class. They have their background abilities, their racial abilities, one feat, one proficient save, 2 skills of their choice, and 1 d8 hit die. Leveling provides them more hit dice and increase proficiency bonus as normal for 5e, but that's it.
As the game progresses, they gain the ability to "spend" XP (level is based on the total "earned" XP, so this doesn't slow level progression, contra 3e) during downtime to learn new abilities. Baseline, they can acquire a feat for 1000 XP and a single point of stat improvement (max 20) for 500 XP. (XP gain is normalized to be 1000 XP for every level.) Additionally, magic items, various NPCs who act as trainers or mentors, and other events triggered during play (being infected with lycanthropy, for example) give a menu of options to spend XP on to gain new abilities.
For example, this is a wand that they found in Van Richten's herbalist shop.
Rast Leen's Training Wand (attunement, uncommon)
This foot long wand is made of ebony wood, and is capped with a silver hand holding an amber crystal.
A mental command can make this wand cast light (1 charge) or guiding bolt (2 charges). This wand has 7 charges, and regains 2d4 charges at dawn. You can use these abilities from the wand without being attuned to it.
Attunement Abilities (You can learn these abilities while attuned, and they only function while attuned.)
250 XP - When you carry this wand, it functions as if attuned even if you are no longer attuned to it. Additionally, you can reconstruct this wand if it is damaged for 100 gp and 3 days of crafting time.
100 XP - Casting light from this wand now costs 0 charges.
400 XP - This wand now has 14 charges, and regains 2d4 charges at dawn and at dusk.
200 XP - You add the spells guiding bolt and light to your spells known.
300 XP, level 3 - Every guiding bolt you cast from this wand is cast as a 2nd level spell.
500 XP, level 5 - You gain resistance to radiant damage.