To be fair, this is more of an info-beamer issue. The hardware decoder should in theory be able to do this, but for some reason it doesn’t work yet and I don’t have the in-depth knowledge of that piece of hardware to say what the exact reason is. There is now an official patch to FFmpeg on Raspbian, but info-beamer cannot use that one at the moment as its API is incompatible.
At some point info-beamer will be ported over and it might be fixed by that, but I don’t see this as a high priority task at the moment as multiple HEVC videos is a bad idea anyway as you’re very likely to get lost video signals due to too much load on the Pis video scaler generating the HDMI output. We’ll see.