This may be a stupid idea, but the simple solution I can see with both weapons and armour, is thus: HoW drops, add a couple of extra upgrade slots on to each item. Then, you first have to max the xp requirement for the first new slot; you then have to complete 7 high level strikes to get an upgrade token; apply this token to enable that perk/power/defence slot. You then work on the next one, but you require 2 upgrade tokens (14 high level strikes). This keeps all armour/weapons relevant without having to either re-roll, are re-grind. You can then choose to use the new HoW gear and grind to get that fully levelled, or stay with your existing gear. The HoW armour will have different perks, and offer 30% more defence. HoW weapons will have 15% greater impact damage.