This could be mixed nicely with another feature that has been requested
once and awhile:
composite time signatures (or compound timesignatures as I also have
seen). This is used in modern church music. This could be specified with
something like '\timeset { 4/4 3/4 }'. This triggers the follwoing
behavior:
1. At the point of definition the time signature are printed.
2. By default the actual time signature is set to the first signature in
the set.
3. When a timesignature changes within the set i.e. from 3/4 to 4/4 and
back, no timesignature is printed by default.
4. When a timesignature changes from something in the time signature set
to something outside it, then the timesignature is printed by default.
5. When a timesignature is changed from something outside the set to
someting in it, then the time signature is not printed by default.
6. An empty set reverts the behaviour to the normal lilypond behaviour
with the currently active timesignature, which is then printed by default.
7. All items mentioned before as 'by default' are tweakable properties.
If the extra '\time x/y' statements are too much to type one could also
think of using the "|" to simplify notation, although this leads to
overloaded usage of the "|" symbol.