The .473 boltface dimension is standard on a TON of cartridges---from .22-250 on up. BUT, you're limiting yourself by using the .243 as a starting point, because it only allows the use of "short action" cartridges.
I've been toying with a similar idea, but I'm gonna use a Savage, because its easier to change barrels, and if I start with a "long action" I can go from .22-250 up to 35 whelen(or beyond), and about 100 (including wildcats) calibers in between. May have to work out feeding issues, but that's OK. AND, you can change the bolt face (as opposed to the whole bolt/action, on a Savage, to add even more (e.g. magnum .532 rim size) calibers.