Adding VLAN interfaces requires command line use. Why not make it possible via the UI? Additional VLAN interfaces are already displayed correctly in the UI once set up, but manual command line setup is required.
HA is not suited for multiple NICs.
Many of the discovery protocols are not routable and can only exist on one NIC, and it can be hard to control which NIC it is in HA.
At the same time IPv6 is coming, which mean you will have the same network names on some or all of your NICs, but they will not be the same network at all.
These things cause many issues among users that try to run with multiple NICs.
If you want multiple NICs then run a core version of HA, so you can control those things yourself.
Especially IPv6 is impossible to control inside HA.