This is also a good idea, IMO. Part of the word of mouth concept, I suppose.
One thing I’ve noticed, though – and I think there’s even science to back this up (but I can’t recall where I heard this, so I could be wrong on that) – is that when someone receives something for free, they tend to value it less than if they had to pay for it themselves. The ‘concern’ would be that people who receive a sub (lifetime or regular) may end up not even using it or, alternatively, having a lower opinion of it (less likely to give positive review/recommendation).
I don’t know how ‘serious’ or realistic this concern actually is, though! Just mentioning that I heard something like this before. Maybe it wouldn’t apply to Bunpro?
One way that might work to ‘mitigate’ this potential concern could be to do as you say, and try to confer such gifted-subs to people who are already interested in using Bunpro, such as forum members, or randomly chosen from those who already have monthly/yearly memberships.
Might be cool on the user-experience side of things if someone with an existing monthly/yearly subscription logged on one day and got a celebratory splash-screen / banner saying,
(With a little simple animation of party stuffs, like the new WaniKani Level-Up banner.)
"
Hey! Wow! That’s awesome!" they might say. In which case, might also be a nice user-experience thing to have a way for the recipient to send a thank-you note back to the donor.
A tip option might also be fine, in addition. Not sure if it detracts from the gift option or not.
On many streaming platforms, both options are available usually. Although maybe not a straight ‘tip’; usually you ‘get’ something for the tip, even if it’s just a ‘superchat’ or just a notification to others that you’ve tipped.