I don't actually have tagging turned on but I was here anyway :)
If you're 7kg off the weight limit of the spin seat and don't need it for another baby, I'd just wait. DS2 has just had his 2 year check and he's gone from being off the charts to just over average so I actually think he may be fine now in our Joie 360. Maybe you'll find similar happens to you :) No harm in doing research of course in order to be prepared if/when he does need a new seat but I would hold off buying it until you need it, especially if you like the spin feature (the recline also tends to be less flexible in bigger seats).
I don't think Britax are due to bring a new ERF seat out. I could be wrong but I don't get any vibes in that direction. Joie maybe... they keep hinting at it but if they are they are keeping it v much under wraps. You tend to get the big baby shows in September/October and new seats will be unveiled then.
The two I do know about are Axkid One which is a new isofix seat up to 125cm and 23kg (very expensive) and Klippan Opti 129 which is a seat that is approved up to 125cm and 32kg, which is the highest RF weight limit in the world. These are both under the newer regulation which is less constrained in terms of weight limits so you might see more interesting seats along these lines over the next couple of years. I would not be surprised if Concord extend the height limit on their Reverso. That would be much more affordable than the Axkid One.
The problem with spin seats for bigger kids is they get really unwieldy, especially if you want them to rear face - their heads would be touching the ceiling! The 25kg seats have the kids sitting lower down. They can generally climb up themselves from about 2 years old because of the base of the seat being lower.
Another lower cost option you could look out for is a forward facing seat which harnesses over 18kg. These tend to need top tether. But they are becoming really popular and I would think more will be released over the next year or two.