Is it the last batch of auras, at least in terms of the skill-based ones (i.e. 10% bonus auras)?

Currently yes.

In terms of future updates? We don't know; one could assume it might be the final tier of any future auras seeing as it has used up all the graphical pips around the auras that signify tier and equally anything more than 10% is getting a bit too powerful for something which in Jagex's own words (when the scheme first came) is meant to offer a nice bonus but not become a necessity for any game content.

We can assume it is because it fills those four red dots on the corner of the aura icon, but we don't know for sure if they'll come up with something new... They can just add T5 and add more color to it or something, honestly I don't think they're the last though