With this sort of thing, you have to be very careful what you wish for. Give specifics as well.
Though its always better to have more buttons than less, since atm there's hardly any that would need merging.

Merged buttons I would like

About half of monk's either useless or overly niche skills (seriously 5 things to do when boss is disengaging is too many)

Ley lines and Between the lines. BLM's have been asking for this for ages.
Cover and intervention.
Hide and Trick attack
Dragonfire dive and Stardiver. They are literally the same just potency. Dragonfire is on too long a cooldown anyway
Draw and play (seriously decoupling these was a stupid idea like many things in current Astro. Just remove the timer)
Cure 1/benefic 1 into cure 2/benefic 2. Benefic 1 is never used and Cure 1 is no longer used after level 40