Can and should are two different things to consider in this case.
When it comes to discographies, Wiz Khalifa's is pretty complete. He's been around long enough and recorded a few classics. Kush & Orange Juice and Rolling Papers will forever be some of our favorite works from him and while his recent work arguably has not held up to the standard put forth by his previous albums, Wiz is still working at a quick rate. He's always down to experiment with his sound too, which is something that other veterans of the game are afraid to do. As he plans out his next major release, he asked fans if they think he'd be able to pull off a full album of just singing and no rapping.
The Pittsburgh artist wrote, "COULD I MAKE AN ALBUM🎶 WIT ME JUST SINGIN," and fans responded enthusiastically. In this case, could and should are two separate entities to consider. Can he make an entire singing album? Absolutely - what's stopping him? Should he, though? That's the real question. Wiz does not have the widest vocal range but he can absolutely pull off a few singing tracks on his projects. He's proven to actually come out with a few hits when he goes for a softer tone actually.
His fans seem to be behind the idea, encouraging him to do what he feels is right for the next project. If that's singing then go for it!