Quote michèle 2
Isn't it a subjunctive form?
No - English doesn't have a subjunctive as such. The same idea would be expressed in other languages (eg Italian) with a subjunctive form, but that's just how those languages express the concept of a wish. In a sense it is a command - or at least, grammatically it's an imperative. It's connected to the use of may
in English to express possibility of occurrence and could be glossed as "let it be possible that ..." or "let it be the case that.." If you turn it back into an ordinary affirmative which expresses possibility in the sense of permission you can see a connection between the wish and the statement - for example : Yoda : Luke - trained hard you have and ready to become a Jedi knight you are. Passed you have - and from now on, the force may be with you.
ie Yoda "consents" that the force may be with Luke- "you are permitted to have the force with you". Turn that into a wish and, as I said you get something like "let it be the case that ..."
Clear it is I hope ...
As for Mesmarks query about other expressions, some which stagger to mind include : May you rot in hell (sorry but you did ask), May I never live to see the day when ..., May all your problems be little ones, and the Clapton song : May you never lay your head down without a hand to hold, May you never make your bed ... May you never lose your temper if you get hit in a bar room fight ...