I’ve occasionally used P2 DVCPROHD media on a classic Nitris (just a short test), and as long as you have a really fast CPU, it seems to work.
Thing is, as said, DVCPROHD is thin raster, and this means that upon output, the footage needs to be scaled to full raster. The DX boxes have hardware to handle this, all other boxes do not.
Ever since MC/SN v.3, the architecture of the software has changed, so that various tasks can be distributed over GPU, CPU and hardware boxes. This has caused increased performance overall.