Triggers on transaction?

I found myself in need of triggers that are run only once per transaction,
rather than per row or statement within the transaction. Meaning it will
always be deferred and never called twice for the same transaction.

Perhaps in 9.6 this part of syntax for trigger creation can be changed from:

[ FOR [ EACH ] { ROW | STATEMENT } ]

to:

[ FOR [ EACH ] { ROW | STATEMENT | TRANSACTION } ]

I looked though the code get an idea of how difficult it would be to
implement and I think I might be able to do it, at least for functions
without parameters. My idea for functions with parameters is to have them
constrained to each one only accepting arrays of the type of element that
is passed. Meaning if the column type is integer[], the function must take
integer[][] in that parameter. From then on it's a matter of choice whether
they'll be passed at original order or reverse and whether the trigger
execution will be moved back or not.

Should I bother trying or will such a feature not be accepted into a final
release, even if it's working?