Presuming you don't run into any snags with the floor joists being in the way, then I don't see any problem in putting in an offset tub drain.

Offset drains are used all the time for sinks, in nursing homes or hospitals for example where the person using the sink is confined to a wheel chair and a regular P-trap under the sink would be in the way. In fact, a tub drain is NORMALLY offset because the flow down the drain and down the tub overflow spout collect at a tee before both flows go into the p-trap. So, all you're doing is making the existing offset an inch or two longer, and I can't see why that would be a problem.

PS:
If you take baths instead of showers, it's a good idea to keep a 5 gallon pail handy. After bathing, pour a full 5 gallon pail of dirty bath water down your bathroom sink drain. Drains clog gradually, and putting maximum flow down the bathroom sink drain periodically keeps it clear. And, of course, it's a good idea to use that grey water in the tub to flush your toilet. If you flush the toilet normally before or after a bath, you refill the tank with cold water, and in a room filled with warm humid air, that results in the toilet tank sweating and puddles of water under the tank on the floor. These puddles are often presumed to be a problem with the toilet leaking.