Early drafts of the set felt like they were lacking focus as the mechanics were spread too thin. As a result, I've decided to lay down the following guiding principles for where the mechanics should appear.
Siphon - All colours, but green/white creatures must not be druids
Discharge () - UR (Wizards) Primary, WB secondary, none in G
Infuse () - WG (Druids) Primary, UB secondary, none in R
Vanguard () - RB (Warriors) Primary, WG secondary, none in U
Survivor () - UG (scouts) Primary, BR secondary but no clerics with survivor
Lineage () - WB (clerics) Primary, all colours secondary
Cycling () - WBR subtheme, UG permitted (especially for cycles)
If you come across a card which goes against this roadmap, flag it in a comment!