I think the main thing we have to remember is the designer's intentions. In this case, it is to give players the idea that humans are more skillful or adaptable without the use of feats, which some people don't want to use, and skills, which some people don't want to use. They want to keep a very basic game without customizable fiddly bits for people who don't want them.
...
That is my alternative. Critique it and suggest your own.
I'm not going to critique your proposal because I made the same in another thread
But I want to elaborate on the section above from your post. I agree on the designer's intentions. OTOH I ask myself... how many groups are
really not going to use skills and feats? Maybe I'm totally wrong, but IMHO the vast majority is going to use both. And the minority who is going to use neither skills nor feats looks like it will be comprised mostly of "old-schoolers". But how many of those old-schoolers are going to say "no skills in our game!" (which by the way in 5e are nothing but simple bonuses to some ability checks, not the large and complex subsystem of 3ed, so they are probably more acceptable now than before to an old-schooler) and "no feats in our game!" (feats being simple additional abilities) but are going to say "yes to super-humans with +1 to every score!"??? Why would a group of old-schoolers refuse to use skills and feats, but still play 5e with mandatory stuff like cantrips at-will, rituals at-will, expertise dice, sneak attack, turn undead as a spell, and a lot of other built-in details that have little to do with "old-school"? They'd rather not play 5e at all, but if they don't, it certainly won't be because of skills and feats... There are things in 5e which will make an old-schooler run away, and skills and feats are the
least of them.
Therefore IMHO the groups who aren't going to use skills and feats are not really the old-schoolers' groups... they are more likely going to be
beginners' groups which choose to play their first campaigns with the smaller number of options so that it's a bit easier. If they get hooked in the game, skills and feats are
much easier to learn (skills = flat bonuses! feats = simple add-ons abilities!) and use than the expertise dice or the sorcerer's willpower mechanic or other class-specific features that by default
cannot be removed, therefore the same beginners groups most likely they
will later use skills and feats.
All this to say that IMHO the best thing to do (since I am myself uneasy with the XP bonus idea, even tho I suggested it) is
just give Humans bonus skills and feats.
Then put a nice sidebar which says "if your group doesn't use skills or feats, consider the following alternative bonuses to Humans" and propose the +1 to all abilities, an XP bonus alternative, and even something else.