Source for them saying you can earn artifact transmog after Legion for non-artifacts, please?Right. The more there is to do the more you have to do. That doesn't stop the fact that towards the end of the expansion if will be way easier then it is right now to do all of those things. It is still alt friendly. There may be more you have to do then other expansions but that doesn't translate to being alt unfriendly because you always had to do stuff on alts to get stuff. For example tier drops. You had to do the raid on that class and get that token/tier to drop in order to "do everything on an alt".
Blizzard has already said that appearances will not be legion only. They have said that eventually everyone will get the 7.2 challenge appearances because the encounters do not scale. Artifacts are "legion only". And look at the hidden appearances for an example of what Blizzard could do. They reduced the requirements needed to unlock the variants because of the new challenge appearances.
That is making it friendly for alts to unlock all of those.