Although TiddlyWiki formatting is different from many other Wikis, its format rarely conflicts with those of other Wikis. (See
http://www.wikimatrix.org/ ). One notable exception is strikethrough "==". TiddlyWiki is the only wiki of the 57 currently listed at wikimatrix that uses "==" for strikethrough. And "stealing" it in this way means it is not readily available for other uses (heading is the most common usage of "=...").
Strikethrough is a fairly rarely used format, so Jeremy and I agree that the impact of changing strikethrough to stop using "==" is probably be small, but we thought we should ask the community.
See here.