Thanks for the speeds info.
I doubt DB would want 200kph stock on a 249kph route in a Taktfahrplan.
I assumed that EC164/165 would switch to Tauern-Villach-Koralm as it would be faster (see the Koralmbahn thread) and ISTR that the service was planned to switch to RJ in a couple of years anyway - but again I may well be wrong.
There are no plans to switch this service to RJ - not enough sets and the use of SBB coaches is essential to balance RJ workings from Vienna to Zürich (Austrian-Swiss cross-border traffic is, thankfully, still run in the old-fashioned cooperative way).
If the service survives the Koralmbahn at all (and the PSO obligations seem to require it), it will most probably be on the current route, and that is also the current plan. As all such long distance services, intermediate destinations are very important, in the case of this train more than all, since demand between Zürich and Graz is not really huge. Instead, the train serves quite an important purpose in bringing Swiss tourists to Austrian holiday destinations. - the Swiss like traveling by train, and Austria is a much cheaper destination than Switzerland itself,). Of course, these plans are still subject to change.
@Germany: I just had a look at the Deutschlandtakt plans again, and Karlsruhe - Basel Bad Bhf has a planned journey time of 1h22 (vs 1h34 now). We will have to see how much of the time saving will be achieved by new line segments and how much will really rely on running at 250 kph (with stops about every 20-25 minutes, probably not much: more will probably depend on the use of rapidly accelerating train sets... same result though, since it excludes LHCS).
In any case, the Rheintal will not be ready for quite some years. The panorama coaches will probably be withdrawn by then anyway...