I'd be fine with something like that. Honestly, I don't think the blast master is all that terrible as-is; just dragging a bit behind similar weapons with 9th edition books. The profile you've suggested would be a modest-but-reasonable improvement on the current statline that would make it slightly better against most
meq infantry.
That said, what the blast master looks like should really depend on what gimmick they end up giving sonic weapons, and I think those might be in for an overhaul. Ignoring cover was great back in the day when cover saves were a thing. Now, it's basically just an extra -1
AP that only kicks in against units benefitting from light cover. Compared to the always-on
AP of inferno bolt weapons or the benefits of plague weapons, that's kind of niche. So I could see them getting an entirely different gimmick more inkeeping with the times.
Eldar vibro weapons just had their special rules removed rather than turned into an interesting gimmick, so maybe sonic weapons will just get a
raw power boost. But if not, they could go in a lot of interesting directions. Weapons that get more powerful the more consecutive turns a unit is targeted by at least one sonic weapon. Weapons that get more powerful based on how many sonic weapons have targeted them so far this phase. Sonic weapons that apply debuffs as the sonic effects rattle your system despite not killing you. Sonic weapons that get more powerful when their target is in terrain because the structure gets used as a tuning fork. Lots of possibilities.
So if sonic weapons do get some kind of neat new special ability, I'd expect the blast master to tie into that gimmick in some way.