I'm getting ready to do the exact same thing. I bought an extra 6004 for the G23 and X300. With the end cap popped out, it fits the X300 U and X300 V. With dremel work, I am going to try to modify the top of the holster to fit up with the RMR. I, too, believe the hood will clear. I'll post up pics if I get it done before you.
I ordered a 6354 DO as well that I'm told may work. If it doesn't work, I'll sell it.
I confirmed with Blade Tech that their WRS will NOT work with the X300 U or V. They said they would contact me if they made one that would.
I confirmed with GCODE that their SOC will NOT work either with the X300 U or V. They said they would contact me if they made one that would.
Safariland customer service has been totally helpless - instead referring to their holster compatibility chart. Their customer service folks clearly have no clue what I'm talking about. They also had no information on whether the 6354 DO would work, but I found a vendor who said it would so I gave them a shot.
Unity tactical had a few companies making belt holsters for it, but nothing level 2 or better. Off The Grid Concepts was one.
It is always a challenge to find a solution for a new gun configuration with new accessories.