Good idea, a marketplace like the tutor section for left over limit could be useful.
Or a donation system where some of our monthly excess limits can be placed in a pool for everyone else to use or even manually donated to someone who needs it occasionally.
Or Normal user can upload courses/lessons, set a option to request for transcription (with a price/credit/free) , Premium plus users can go through a page with such requests, transcribe them if they have excess limit.
Or a lucky draw system where the winners of certain challenges get credits or a free 1 month premium plus.
On an another note, I was thinking that even an ADs based model could be good for those who want to opt into it. I acquired (I wasn’t even trying to learn it) basic conversational mandarin as a kid by watching Chinese series and adverts on TV in chinese during commercial breaks (they repeat alot and adverts tend to be catchy).
So if LingQ has an advert section in our target language to earn credit these can be spent on transcription and etc.
As for me I did some math, cost benefit, I won’t need the plus service, I am already setup with my current queue of materials to consume. Currently I have 3 long book series (with audio) which would put me at over ~2.5 million words read, ~5million if I read twice(+podcast and etc) when done. Cost would be $150ish for the audio or less if I can get family members to sign up for audible trial.
Based on thread by Chytran 5+ million words read would be the milestone to reach. 3-4 million based on hiptothehop experience.
Even if I need premium plus quality transcription or TTS, it will be rare.