3G HD-SDI and ATEM?

I've just started putting together a broadcasting system and have been trying to stay with SMPTE-424 for my long cable runs. But it doesn't look like I can use the ATEM series switchers with this.

Can this be added with a future firmware update or is there a hardware limitation keeping this from being supported?

It would need upgraded hardware. Firmware won't do it.

What do you mean, you have been trying to stay with SMPTE 424M for your long cable runs? You can use SMPTE 424M-compliant connectors and cables, you don't need the hardware to support SMPTE 424M unless you are actually running 3G-SDI from your sources to the switcher. I'd recommend to install SMPTE 424M-compliant infrastructure, and upgrade the hardware when needed.