That's why living weapon is such a sweet, sweet mechanic. If only they had printed more fun and balanced equipment besides Bonehoard. Batterskull is silly with its return to hand clause, and the rest is virtually unplayable because way too expensive.
I've tried a few pieces of living weapon before, but they're notoriously hard to grok.
They also have the same problem most artifact creatures do in that they have to make sense in all 5 colors.
Here's the two I had (Rather blatantly stolen from someone on these boards, though I can't remember who. It's written down in the card notes I don't have on me at the moment)
2
2/1 haste
Equip 4
3
3/1 flying
Equip 5
You have to be really careful with the equip cost since it's mostly the only outlet you have for balancing, since the mana cost needs to be kept low so that they're playable as just creatures.
Equip 4 is there on the first one because something like
lightning greaves makes a lot of people die when they otherwise might not have, and if lightning greaves turned 1 and 2 drops into sizeable threats, it would be a broken card indeed.
The average aggro deck can probably expect to have 5 lands in play at their end game, and maybe 6 at a pinch. 5 will let you play and swing with a 1 drop (that likely has 4 power now), but the prospect of swining with a (likely 5 power) 2 drop creature is a little less guaranteed. We all know how important the difference between 4 and 5 power is, after all.
The second piece is designed less around playing and equipping to a creature, but rather more around having creatures in play and using this to jump past blockers.
5 is enough that (again, based on the descriptions above about how much land your average aggro deck is likely to have) you probably can't equip this, swing past someone's board, and then deploy more pressure. You either equip this or advance your board, not both.
I'm not 100% on the numbers, since it's been a while since these cards were in my cube (Again, hard to grok and the haste card did feel really out of place in blue/white aggro decks, for eg) so feel free to correct me (I didn't change the costs from whoever I borrowed them from, and again, sorry about forgetting your name. Should magic set editor ever come out for Android this will become much easier)
It's very desirable design space, for sure. But it's hard to come up with playable french vanilla creatures that fit every color. As well, the reminder text on living weapon (as well as bestow) is not insubstantial, which means the creatures need to be simple for font size reasons as well.