For me one year is fine as a deprecation period. I feel that sites
should be kept stable when working, and then, after maybe a year or
two or more, when needed, moved to a new and updated system. If you
then have special software, you'll need to update it.
If we want those types of updates to work without software changes,
then we need deprecation periods that are 3-5 years, which I find
wholly unreasonable. I tend to think two years is a bit long, but 1,
1.5 and 2 years are all acceptable to me, though I definitely would
prefer 1 year. That also coincides nicely with the 2 version policy we
have run so far.
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