Lab Rotation offer, but may be unable to take graduate students

[Souzou]

I will be starting a neuroscience PhD program this fall. Has anyone ever done a laboratory rotation in which the professor could not "guarantee" they can take on graduate students for dissertation research (whether due to funding or already having too many students)? Is this an issue? I really enjoy the research this professor is doing and I think we appear to be a good personality fit. I am nervous about doing a rotation and enjoying the research, only to find out the professor actually cannot take me on as a dissertation student.

[ss2player]

I posted a similar question recently: 

 

Came to the conclusion it's probably not worth it, but I have people whom are more sure of their funding situation. If you have more of a chance this becomes murkier.

[Souzou]

I remember reading your thread, and the responses were helpful. However, I feel that my situation is a little "murkier" because this professor may (or may not) be graduating students this year. If he does, then I would be able to join the lab. If not, the lab may be too full for me to join! He seems to want me to rotate there and potentially be his graduate student, but the professor has repeatedly told me he cannot "guarantee" anything.

[ss2player]

I see...can you contact the graduate students and see how their progress is going? When they might defend? Good to get information from all angles, sometimes profs can be a little frustrating with their transparency. But go through the prof, you could say "I'd really love to rotate and join the lab if I like it, but I need to know my chances first. May I talk to the students in your lab about if they might graduate this year?"