Interesting that the article says nothing about salaries and available positions. And, also, at the end, the article mentions that Fujitsu is finishing with mainframes in 10 years. Young people are smarter than going aboard a sinking ship.
I think people are reading more into this announcement than it actually means.
Fujitsu has three mainframe lines: GS21, BS2000, and VME. The announcement it links to is only about GS21 hardware, not BS2000 or VME.
GS21 started out as clones of IBM mainframes, including both Fujitsu's Japanese clone line, and also Amdahl in the US. In the 1980s thru the first half of the 1990s, Fujitsu's Japanese clones were popular in some countries outside Japan (e.g. Australia), and Amdahl's clones enjoyed a lot of popularity in the US. However, while IBM's own mainframes went from 31-bit to 64-bit in 2000, Fujitsu's GS21 line got stuck on 31-bit. AFAIK, nobody uses it anymore except in Japan, non-Japanese customers either migrated off the mainframe or switched to IBM. In Japan, it clings on in government and some large corporations, but is deeply legacy.
BS2000 has a very different heritage. RCA used to sell mainframes in the US. One of their (several incompatible) mainframe lines was partially compatible with IBM S/360, having the same assembly language in user space. However, kernel mode instructions and the software were incompatible. Siemens in Germany bought the rights to it. It ended up surviving in Europe even after it died in the US. Eventually Siemens sold it to Fujitsu.
VME was originally the British mainframe manufacturer ICL, which Fujitsu ended up buying. The British government is (I believe) the only people still using it, and they've been trying to get rid of it.
Both VME and BS2000 haven't had their own physical hardware for years now – they are just software emulators running under Linux or Windows. As such, they are easy to "migrate to the Cloud". Fujitsu is likely to keep on supporting them (to some degree) as long as there remains at least one customer willing to pay enough $$$ to sustain it. Given that, any timeframes for phasing either out should be taken with a large grain of salt, since their future really depends on how long it takes the remaining customers to get off them.
Coming to this GS21 announcement – I understand Fujitsu wants to stop manufacturing and selling physical mainframes in Japan. They can just switch to software emulation like they do for BS2000 and VME. Like both of those, it can run fine in the cloud, and I expect they'll keep it running as long as there is customer demand. Promised future support timelines are very notional, if there is a big enough customer paying for an extension, the extension will happen. Plausibly, it could still be supported in 20 years time – maybe it is used by some essential Japanese government system, and the Japanese government's repeated attempts to migrate to a more modern platform end in failure (not an uncommon story for government IT projects)