This was discussed by Ven Brahmali elsewhere. The ending is dative/genitive feminine singular.
It has most commonly been read as:
- sabbattatāya = sabba + attā + tā = all + self + -ness = “to each as to oneself”
However from the context it is very likely to be:
- sabbatthatāya = sabba + -ttha + tā = all + place + -ness = “to everywhere, in every respect”
Here “-ttha” is a secondary pronomial suffix, having the general meaning of “place”.