Probably bad for the lowest fares in the market, but some legit competition for the majors (even if B6/NK combined is still meaningfully smaller) can't be such a bad thing. I don't think AA/DL/UA/WN ever really matched NK's fares because they're targeted at different segments (and also because the fares probably weren't really much lower after all the nickels and dimes), but there is definitely more crossover with B6.
And of course "legit competition" remains to be seen given the managerial *@$%show at B6. But sounds good in theory!