ngl, i feels “weird” for me to see people lament the “powercreep introduction” tied to a specific feature
but not lament regular powevercreep 
where’s the grandpa shaking hand at clouds “every” patch update that adds more and more player power? or for that matter just by virtue of an expansion happening and new/more items and points etc occurs?
idono, maybe it’s because i haven’t had my morning coffee yet, but reading through some of the posts i had this sensation “you’re all wrong”, and also arguing for nothing, but maybe i’m biased and or grumpy to not see the whole picture.
For me this feature boils down to, will it trivialize obtaining cool items “too much”, eg how legends don’t feel awesome because we drop 50 every time we turn our heads around. And if it does trivialize it, does it do it to where it feels sadge.
My assumption, not being a playtester, is that Crate has some sort of ratio in mind, similar like how even if we drop loads of legends we might not be dropping the exact ones we want or unique legends have a fixed 5-10% drop rate. Further assumption would then be initially players, just like with legends, feel the ratio is too low/stingy, costs too many mats or too much rng involved getting the affix transmutation “to our desire”, and might increase it later, “further trivializing the items”. That’s simply just judging by past player reactions and Crate’s response to alleviate those requests.
But, that still might not mean it’s going to be bad, because even if regular legends are voluminous and i feel not special in drops, i do appreciate what they’ve done for unique legends drop rates being increased.
I’m going to assume the affix transmutation will end up similar “by design” perhaps even. Some stuff will feel abundant, but the alkamos ring equivalent affix combo will feel nicer even if not totally non-grindy.
As for the powercreep introduction tied to this specific feature, oh boy, if the last expansions is anything to go by, affix rerolling should be the least of your concerns if you dislike powercreep
edit, someone just posted this, and if anything it should probably highlight the reason for this feature, and why it might even be “needed” (depending on OG arpg’er sentiment or not ofc)
the features concern isn’t about adding powercreep(from dev side), but basically “QoL” to a large segment of players, as is Crate’s way over the years
QoL then trumps the powercreep concern i suppose we might say,
and if stuff gets too powerful you can always advocate for Zantai’s nerf 
in future update PTRs, he would probably love to swing that 