And it generally starts to become a hassle as soon as 2 or more Addons use actionIDs...
Yup... I have (on my druid) two bars for caster form (a healing-oriented set and a more well-rounded PvPish set)... a bar for bear, a bar for unstealthed cat, and a bar for stealthed cat. They are all 12 buttons, so right there that's 60 buttons. To make matters worse, they aren't in a consecutive block of 60 (because I believe the default UI doesn't have them in consecutive blocks, and I want to be able to use the default in case something happens before a raid or something and I need to ditch my mods). I was already allocating another 25 buttons to Geist... that puts me at 85 IDs already, and confusingly laid out.
I -did- manage to find the IDs I need (luckily I don't use Klappa on my druid, only my warlock) thanks mostly to autobar handling more and more of my less-frequently-used abilities (summon, ritual of souls, stone conjuration, etc) that I don't mind clicking, but yeah, in my opinion the move to use IDs makes the addon a lot less flexible for a lot of us.
That said, you should write the mod for yourself first, and if it works out best to use IDs, then go for it. There are older versions and other mods for those of us with stricter requirements. I mostly reiterate what was already said to reinforce the idea that there are many of us who greatly appreciated the work you had previously done with ID-free buttons.