While Airbus have a variant of the A330neo under development, it’s not currently available.
Actually Airbus already begin to offer that. In last presentation with Indonesian MinDef, they already offer this variant to Indonesia as A330 MRTT Plus. It is base on A330-800 Neo. They are begin to market it as they also have problem with Airlines mostly want to buy A330-900 Neo while A330-800 Neo is significantly lagging behind in order then it's stablemate.
So basically it is already in their official production line up, it's just no takers yet. I suspect they are offering to Indonesia in order for Indonesian Government to take over Garuda Indonesia order of 4 A330-800. As from what I heard Garuda seems want to change that order to the much more popular A330-900 which already entering their fleet anyway.
Add:
Specs on A330 MRTT+
Airbus Defence & Space's next multi-role tanker transport (MRTT) customer will be the first to acquire the capability integrated with the A330-800 airframe, with deliveries expected from late this decade.
www.flightglobal.com
Airbus expects to deliver the first of its A330neo-based aerial refueling tankers before the end of the decade through the MRTT+ upgrade.
aviationweek.com
So by end of this decade, not really far away for those who order Tankers now. If you already have A330-800 Neo on order or taking over existing order, perhaps it can be faster.