Re: casting in armor, the base 5e ruleset lets you cast in armor so long as you have proficiency with it, it's just that Wizards and Sorcerers don't get any default armor proficiency (unless they burn a feat later on). IMO, it's just an extension of the general "if you're not proficient with an armor, you don't know how to use/move with it efficiently, so you're at a disadvantage as long as you're dealing with the unusual weight/sensations" with a side of 'spellcasting already involves juggling a whole bunch of physical, metaphysical, and mental processes, if you're already off-balance due to armor you don't know how to wear effectively, you probably can't keep all those factors going at the same time'.
Which is perhaps a very forgiving explanation/interpretation of a rule that ultimately boils down to 'well, arcane mages don't get armor, traditionally, so here's how we do that in this new ruleset', so. mileage may vary.
But def agree with opening up more appearance options, both picking 'theme colors' and (maybe) extra models for outfits.
