Heads will be fully supported with the Librem 13 v3 (the next revision) and the Librem 15 v4 (the next revision). We will be adding the hardware TPM to the motherboard, which is the last component part that did not make it into our current revision. The "next revision" in this case is the exact same as what we are getting into inventory in May, but adding the TPM to the motherboard (and possibly an IC for USB-Type-C video (unrelated to Heads but related to the fabrication of the motherboard)).
So Heads compliant hardware for the Librem 13 and Librem 15 will be in our second inventory order, which should arrive around September, 2017 for both products. Note: Heads runs on the current hardware, but without a TPM it is not helpful.