i don't have first hand experience with the rotel/systemdek, but i read elsewhere that the rega sub-platter and platters will not fit on them.
here's the post i saw previously, in a thread on the vinyl asylum:
https://www.vinylengine.com/turntable_forum/viewtopic.php?f=32&t=46161#p360067
and a pic of the systemdek i920, (the one like the rotel) from that thread:
rp900 w/systemdek(?) acrylic platter;
and, if the parts are not interchangeable between the rega and the rotel, it does seem that you can easily swap out the bearing assembly to accept rega upgrades, as they are readily available, both stock and upgraded. i stumbled across this site; it seems you can make these rega decks almost totally unrecognizable from stock:
http://lpturntables.blogspot.com/2011/09/list-of-upgrade-accessories.html
(stock rega subplatter/bearing assembly):
https://www.amazon.co.uk/Rega-RP1-Replacement-Bearing-Assembly/dp/B00INUXVC8
interestingly enough, it seems that rotel made two completely different turntables, both labeled "rp900"
doug s.