So with the addition of the Roarmulus twins a while back, we finally no longer have a boss-free gate, and are now facing a distinct shortage of non-boss Stratum 4 areas.
My suggestion would be to combine the bosses on a given stratum into a single gate, and have the elevator at Basil select between the different bosses. In fact, you could even fix up the elevator to the left of basil and have it so that, say, if you go down the right elevator you drop into the RJ levels, and if you go down the left you drop into the RT levels, or something like that, and more elevators could be added if the boss count increases. Given that the next level after basil is usually just another regular level or arena (with the exception of FSC, iirc) you're still left with plenty of time for your party to fill up or to invite friends before the boss levels begin.
In the arcade, instead of a theme icon for the boss (like beast for snarby, fire for FSC), the gate indicator would just have a generic "boss levels" icon at that given stratum.
What you forgot is how people who press join party may not like that they'll end up in a different boss gate.
Your idea is bad
Who wants a normal gate?
I for one don't see an upside to your suggestion.
Besides there's going to be another boss coming and what will your idea fix then?
Absolutely nothing.