According to the Android Source information, BT LE 4.2 or higher should suffice for HA connectivity with additional requirements for central and peripheral devices. I think things like the BT 5.0 PHY layer for advertising, etc., would just be icing on the cake, not a required part of the cake. But as MDB says, time will tell and we shouldn’t have to wait long if, as um_bongo posted a while back, ReSound is going to release MFA around the start of the 3rd quarter of 2019.
https://source.android.com/devices/bluetooth/asha#system-requirements
Edit_Update: Actually, the following is from the end of the section referenced above - so the PHY layers are icing on the cake: Notice the MAY language
“The peripheral and central may implement 2M PHY as specified in BT 5. The central shall support audio links up to 64 kbit/s on both 1M and 2M PHY but can choose to limit support for links requiring more than 64 kbit/s to the 2M PHY in order to improve coexistence with other 2.4 GHz devices. The BLE long range PHY shall not be used.”