Sure, but the point of the product isn't just "more of 5E".
At least I am not hugely interested in "more" - I'm interested in deeper. 5E already shovels out new subclasses and just more of everything.
But I'm interested in mechanics that add more decision points to
existing character builds.
Just adding "more" does allow you to create more types of characters, but once you have selected your subclass, having more subclasses does nothing for your existing character.
But if L5E were to (for instance) modularize subclasses into the four tiers so you could start mix and match them, it would do wonders for the customizability of existing characters. That is (to continue this example) you could create a Barbarian character that picks the Totem Warrior subclass at tier 1 and 3, but the fighter subclass battlemaster at tier 2, and the druid subclass Circle of the Moon at tier 4.
Not saying this necessarily is a good idea. Just an illustration to explain my point.
To do this, each subclass (and each part of each subclass) would be standardized to all cover the exact same levels (1-4, 5-10, 11-16, 17-20).
Other things I can easily envision from an "Advanced 5E" game include:
- recalibrating class abilities - at mid to high level the core abilities are just weak. (I remember looking at the Ranger and concluded it got nothing the game couldn't hand out no later than level 12. Yep, every single last of the Ranger level 13-20 class abilities would make sense to gain no later than level 12)
- recalibrating existing spells. Somewhat simplistically speaking, grab three class guides for each class at random. List the spells that all three authors agree are rated red or orange. Then fix those spells. This doesn't appreciably add power to that class, just variety and choice.
- adding (back) a robust magic item economy to help the legions of gamers that struggle with "worthless" gold in 5E!
The goal of compatibility only needs to mean 5E characters can adventure together with A5E characters. It does not need to (and should not) mean that feats must be the same, spells must be the same, and class abilities must be the same.
Sure adding options so each time you previously just got something you now get three choices is better than nothing. But the risk is that such a game will not come across as substantially different (and distinctly "deeper") from 5E, only "more".
Having to learn a new ruleset - especially one that will inevitably share much of the same terminology to the point of confusion - needs to be worth the investment. Just "slightly more options" won't be worth the bother, I fear. I'm worried this project settles for just wanting to capture the same audience as regular 5E with just "more", thus missing the opportunity to claim the place Paizo used to occupy before they went astray with the bafflingly byzantine and super-constrained PF2 game.
But to end on a positive note - I hope A5E have recruited at least one veteran designer intimately familiar with d20. I'm not necessarily thinking of someone that actually worked on d20 mechanics - just playing that game and building a character and experiencing its "the sky's the limit" sense of wonder and freedom (between play sessions, when you decide on how to level up) would be plenty!