[Trilinos] When to deprecate old versions

[maxfirmbach]

I would like to start a discussion related to when we should deprecate old versions of Trilinos. I look forward to your opinions.

I could see that official releases are supported very long, whereas „minor“ in-between updates have a way shorter and restrictive life-time.

[mayrmt]

I would limit the number of supported version, e.g. to 6 in order to control the potential mess of #ifdef statements throughout the code. Yet, I would keep a version for at least 6 months to give sufficient time for updating to the new version (essentially requiring two updates per year at max).

Official Trilinos release could be subject to special treatment, if desired.