We all love your plugin more than words can express. I am sure you realise this by now!
However, the third party Repeater Collapser plugin has stopped working and breaks layouts now with nested fields and so has become unusable.
Field collapsing is not something that would be nice to have, it is something that has become utterly integral and essential and simply has to be built into the core. The more we use and explore ACF, the bolder we become creating fields, filed groups and layouts that are simply unwieldly without a robust collapsing tool.
In my humble opinion this is not something that should be postponed while other things are addressed, this should be absolute top priority and of the first order!