You can already do this and it is done regularly. With or without rockets.
skorp: We have already seen people drive for hours to back door fields, strats, and HQ. Yes, people would up at a spawn and shell a base no matter how long it took and whether they had spotters or not. Since we already have the M4A3-75, which can shell nearly that far already, then we do not need 105mm or 155mm artillery pieces.
I know. That's why I said we already have bases in range.

Our tanks lack a system for sighting at such ranges, especially the calliope on the M4. If the request is for artillery, then it would make sense for an accurate way to sight them. The problem I see is that if we had that then it would disrupt the gameplay we have.
So if we add artillery with the current way of aiming they are useless. But if we make a way for them to be effective our maps become useless. That was my original question to skorpx1.