I have same concern than Pepe QuiCose, but I don't think this problem is new.
I remember a time (I think it was last summer) when on Vassal everybody was playing Vermin in his or her deck. I found this quite boring and I think it's one of the reason I stopped SW during several months.
If me, I would prefer Mercs just do not exist, they tend to uniform difference betwen factions and I think asymetric is more interesting than everyone playing with same mercs.
Now we can decide to not play with them, to use different format (for example Anoir's tournament idea with less used units only is a good idea for diversity) with no or less mercs.
And for the basic decks format, I am also a big fan of it, don't hesitate to propose it to me on Vassal
I don't know yet if everybody will play with same mercs in every factions decks (I think it's to soon to be sure, for example I don't think RM fits that well in so many factions decks), but should this happen, for sure I would find this very boring.
PS: I have more concern about SG and Etch than about RM, but as I said it's too early for my opinion to be definitive, so far it's just an impression.