I'm a chip designer and a chip this complicated takes about 3 years from start to actual silicon so it would have started well before Softbank started their acquisition process of Ampere.
The press release says it was co-developed with Meta who has a growing custom chip team. Normally these chips like Amazon's Graviton or Google's Axion are designed for their own data center use only and rented to customers. This ARM chip sounds like Meta and other companies will all be able to buy chips for their own data centers.
I'm guessing Softbank will get ARM and Ampere to align on future chips or just merge Ampere completely into ARM.
Neoverse V3 is the server version of Cortex-X4 and it is an Armv9.2-A CPU, with SVE2, but without SME/SME2.
The matrix math extensions, i.e. SME/SME2, are present only in the latest generation of Arm cores (the C1 cores), which implement the Armv9.3-A ISA, and also in recent Apple cores.
Neoverse V3 is also used in AWS Graviton5 and in a few NVIDIA products, e.g. in Thor, and it is also pretty much equivalent with the Skymont and Darkmont Intel E-cores, which are used in the Lunar Lake, Arrow Lake, Panther Lake and Clearwater Forest CPUs.