I don't think it is a tricky as one might think. The wording definitely is more open-ended than many similar effects - namely, letting it apply to all healing, rather than healing rolls, or heals targeting your allies, etc. But I don't see too much difficulty interpreting how it works.
Melora's Tide -- has the Healing keyword, but grants regeneration. So if a cleric uses Beacon of Hope and then Melora's Tide, does the latter grant regen (2+5)=7?
No - Regen isn't Healing. They've clarified this at least once before, I think in reference to this specific power, and that it doesn't get modified by bonuses to healing powers.
Lay on Hands -- say you are a paladin multiclassed into cleric, and for some reason you swap out for Beacon of Hope. Now when you use Lay on Hands (it has the Healing keyword), does it grant (target's healing surge value + 5)?
Yes, certainly. It is a power, it is yours, and it provides healing.
Unicorn's Touch -- swordmage multiclassed into cleric (yeah, I don't know why you'd do this, but work with me). Use Beacon of Hope, then Unicorn's Touch. Will the latter heal (5+5+Con) hp?
Yes, certainly. It is a power, it is yours, and it provides healing.
Spirit's Shield (Shaman class feature) -- more multiclassing fun. Would BoH make Spirit's Shield grant (Wis+5) hp?
Yes, certainly. It is a power, it is yours, and it provides healing.
Healing Spirit (Shaman class feature) -- even more fun. Do you grant (healing surge +5) to the target, and (1d6+5) to the adjacent ally?
This one is finally a bit tricky. Does +5 healing mean 5 extra healing total, or per target? Unlike most other bonuses to healing (which might refer to bonuses to healing rolls, or bonus healing to targets of your healing powers), Beacon of Hope says the power itself heals 5 extra damage. Thus, I could see the interpretation that you can only apply that bonus once, though you could choose which of the two targets gets the extra healing.
I'd probably go with a more liberal ruling that each target gets the benefit, but I can see either reading of the power.