Setting up the RX to run on a 45 could be done with a RoadLink but shift performance would probably be bad.
You made some excellent points, but this is the one I'm curious about. I haven't had an RX in hand and I don't have a cassette with anything bigger than a 42 to try it, but...
Any evidence the Roadlink would make it shift worse? I feel like the b screw is mostly moving the guide pulley up and away from the cassette which affects those small cogs more. The chain doesn't have as much time to be 'guided' by the guide pulley when it's pulled up and back. The Roadlinks (I would guess that you are aware of this) keep the guide pulley lower (relative to the cassette) for a little bit better cassette/chain wrap. What I had found was that I could get an 11-34 to work okay with a standard 11 speed Shimano rear derailleur with the b screw pretty jammed in there to clear the 34, but the Roadlink (and backed out b screw) shifted noticeably better on the rest of the cassette. Possibly due to better chain wrap and the guide pulley getting to do it's job a little earlier in the rotation?
Anyhow, I *wonder* if that n=1 experience could be extrapolated for a larger cassette and larger capacity rear derailleur. Trying to fit a 45 (Modified via Wolf Tooth?) cog in a 1x road application does seem a bit screwball, but I'm all for people trying to figure out what works for them. Maybe the relatively inexpensive Roadlink could be the ticket? I would be curious to find out!