Square is a little more than that at 0.778 trillion yen, and you'd have to put a premium on top of that. So probably more like 1 - 1.1 trillion yen. ($7.4 billion to $8 billion)
The 0.7 trillion yen will be shared amongst the divisions. And usually SIE gets less of it.
Reasons it's not impossible:
They are focusing on SIE expansions more specifically.
They made it clear when they were setting up these proposals, that the dollar amounts would be somewhat flexible. If the right opportunity came up, they would spend more if they had to.
So overall, it's not impossible but I wouldn't expect it.
True, they have always reiterated in the past year that should they require more funds that it would be possible to allocate more. If Sony actually did want to acquire SE those funds would be made available for that.
I think they know going forward they don’t need to acquire SE or any other Japanese publisher. Not to mention that it’s not the right time to make any sizable acquisitions anyways.
Studio stake Investments are now the new norm going forward especially for SE as they have stated several times. Just like From Software, Sony will likely invest in some of Square’s studios to ensure those games make it to their platform which is the likely reason that Octopath Traveler 2 made to PS this time around.