In the past, FC form might have been the best indicator of whether a player should make the Test side. But these days, with such erratic fixturing, and tournaments like the IPL which give essentially domestic players exposure to international-quality opponents, you need to use more judgement.
Maxwell's last FC match (other than the tour match) was a single Division 2 fixture for Hampshire vs Worcs. He made 24 in the first innings as Hampshire was routed by, ironically, Ajmal. He followed it up with 85 in the second innings. My guess is that any FC cricket prior to that was back during the Australian summer. In the meantime, he's played for Kings XI in the Champions League and played three one-dayers for Australia.
Is he in good form at the moment?
Who could really say? I certainly don't have much confidence that he has the ability to really stick around and occupy the crease. Even his best innings rarely last much longer than a session. But then, I can't say I have much confidence in Doolan either and he's supposed to be a long-form specialist. If the selectors want to give Maxwell a shot, I suppose this wouldn't be the worst time.