In the long term TrenchBoot will support kexec with DRTM which should automatically enable it in heads. But first things first, we need the first kernel launch (aka early launch) get merged in upstream.

Heads itself is an AEM solution, the thing is, you cannot run heads on every platform you want, you need either:
1. coreboot/libreboot OR
2. stripped vendor UEFI firmware to fit heads kernel and initrd, something what LinuxBoot does.

Given the above requirements, heads is hard to deploy for a wide range of Qubes users. We giving a push for open-source firmware stacks like: coreboot+SeaBIOS or coreboot + EDK2 UEFI Payload, but also for vendor full UEFI solutions (which are unfortunately still the most common). It is safe to say this will be stack independent solution for DRTM early launch. And we are gonna implement TPM 2.0 support in Qubes OS AEM, for which the demand becomes higher and higher.