Presumably the alignment in Hungary via Hegyeshalom will also provide a fast link to Vienna via the existing Ostbahn.
Nothing said about the line in SK/CZ/PL.
I imagine it will link into the existing "high speed" (CMK) line in Poland which starts north of Katowice and is planned to be a 250km/h line when they have fully implemented ERTMS.
I suppose it is down to the ambition of the countries involved, but Railjet speeds would seem to match their networks.
These currently do 230km/h on upgraded lines in Austria, but new infrastructure (Semmering/Koralm/Brenner) is generally being built for 250km/h with new trains expected to match that.
Plotting a route Bratislava-Ostrava-Katowice won't be easy, compared to the empty country north and south of there in HU/PL.
It's also hard to see a high speed line being built in Czechia and not involving Prague.