Consider the fact that the .308, 30-06, .270, .243, 7mm-08 all share the same parent case. I'm sure that there are probably about 500 cartridges that I haven't mentioned, but you get the picture. So it is feasible to be able to switch barrels.
Keep in mind though that if you were to go for a 30-06 and (lets say) a .243, the difference in the length of the two cartridges could cause problems in the magazine. There will be a big space in the magazine that will have to be 'filled' in order to get reliable functioning. A competent G'smith should be able to fashion a filler block that you could remove and replace when needed.
I like the idea of having one rifle with a few interchangable barrels. It offers a flexibility that is very attractive, especially if the spousal unit will only allow ONE gun!
Good luck and let us know what happens!
Unkel Gilbey