I read it like this:
-We will develop it for 360, PS3 and PC because they have a large install base, worth the trouble.
-We will develop it for PS4 because although the install base may not be as large, it's still the leading next-gen console (both technically and sales-wise), and we are possibly getting some help/publicity/support from Sony.
-We will not develop it for XB1 because the install base is not large enough; but possibly down the line, we may develop for it when there is enough number of users, given that a PS4 to XB1 port is relatively easy.
Playstation 5 vs XBox Series Market Share Estimates
Regional Analysis (only MS and Sony Consoles)
Europe => XB1 : 23-24 % vs PS4 : 76-77%
N. America => XB1 : 49-52% vs PS4 : 48-51%
Global => XB1 : 32-34% vs PS4 : 66-68%
