I've ordered a Macro Tech air spindle, good for 30krpm, and fits into my NM135 existing spindle.
This kind of spindle has very little power compared to your 2HP router, but I need the RPMs for engraving.
I thought alot about rigging a router (I even bought the Bosch 1HP laminate trimmer); one of the main problems is bolting the bosch to the side of the millhead would result in a 4" or 5" offset between the NM135's spindlecenter and the bosch spindlecenter - and a bigger router would be even more than 5".
After I bought the macro spindle, I found this: TB-350S spindle from "Wolfgang Engineering" on ebay - half the price, 20krpm (although I'm sure you could coax it to 30k), doesn't require a compressor, unbelieveably good TIR. I'd have to build an NM135 mount for it, but it is short enough, and the NM135's Z-travel is tall enough, that I could probably mount it directly under the NM135's spindle. And again, this is a low-power spindle.
With regards to your "NM200 spindle produces alot of heat in the bearings"... my NM135 did the same, but is has gotten _alot_ better after a few hours of run-in. (I plugged the mill into the wall through a wattmeter, so I can see the exact powerdraw). It now runs cooler to the touch, and draws alot less power than when it was new. Definitely better with age.
Further, once the spindle warms up, the powerdraw drops alot.