What do you think about coexistence of 2.10 and 1.6 sharing VSAM, Master and User Catalog, DFSMS Control Dataset and CA TPX? Do you think we have some chance to migrate immediately to z/OS 1.6?
I think you will be at very high risk of running into major problems if you attempt to share things like catalogs and the SMS Control Dataset (ACDS) between OS/390 V2.10 and z/OS V1.6. For example, PTF UA00440 is required to share the ACDS between an OS/390 V2.10 and z/OS V1.4. The PTF will prevent corruption of the ACDS on the OS/390 V2.10 system when it is shared with a z/OS V1.4 system. You run the same risk with a z/OS V1.6 system, except that no similar PTF is available. Similarly, there is a good chance that the format of VTOC, VVDS and other control records may have changed. Attempting to share resources between z/OS V1.6 and OS/390 V2.10 is entirely at your risk (and unsupported by IBM), so if you end up having problems, you'll end up the proverbial creek without a paddle. It's a risk I'd never run.
As for TPX compatibility, you need to contact Computer Associates for a definitive answer, but since it is a VTAM application, I think your chances of coexistence/fallback support are much better.