Closest you're going to get to a single set-up is a Colt LE901. You can swap the 7.62/.308 upper for a standard 5.56/.223 upper and use their magwell block to shoot the smaller round.)
And you could very easily get both for that money! But yeah, the 10 and 15 formats are different. You can run 223/5.56, 7.62x39, .300 AAC(Blackout) and many more caliber uppers on a 15 lower and the AR10/LR08 Will house a number of bigger calibers (7.62x51/.308, 6.5 creedmore etc.) just do your homework, check compatibility and take care when taking them out to shoot if you run multiple calibers off the same lower.Thanks for info! But I googled the LE901 and its MSRP is $2600. For that price, I'd rather get an AR-10 and an AR-15.