Assistant Professor at my state university, Research Scientist at my Ivy League, or both? I am a Research Scientist at an Ivy League. I have been offered an Assistant Professorship at the state school. The Ivy League has suggested that if I take the professorship, I could stay on in a 20% role and continue my present research. The state school seems amenable to this arrangement, and would credit my past time here toward tenure, and the ongoing 20% as a tenure-admissible external collaboration.

Within my network, I cannot find a single person with this kind of arrangement. Are joint appointments an uncommon thing? Pointed questions:


What might be the unanticipated issues of joint appointment at different ranks (asst. prof. and research scientist)? 
How can I frame this relationship such that my tenure committee is positive about the arrangement? Any other political considerations?
Is it generally permissible to write for money from two institutions, in effect to be your own subcontractor?
The department at the Ivy is much more highly ranked than that at the state school (top 10 vs 80-90s, engineering). When I move to my next position, how will the time at each institution likely be viewed? Will the Research Scientist role even be considered? Worse, will it be fairly necessary for such a move, such that I dare not let it end?
There is nothing against having a joint appointment. I would take both! At 20%, you gain from networking at the Ivy, and show up once a week...or even half day to attend faculty meetings or seminars. However, focus your research at the State school. In return for 20% support, you must co-list the Ivy in pubs and seminars you give. I’ve done this before, and it’s not hard. Good luck!