I think this would be a great idea. For people that have multiple alts, not having map completion can really make playing them less attractive. I almost exclusively play my main in open world pvp, because, while I have an 80 of every class, the highest map completion of any of them is ~70%. I loved map completion the first time I did it, but I don’t have a ton of interest in doing it 8 more times. I think this would be a great way to help encourage people to play their alts more.
Also, I believe they already have the capability to do this fairly simply since beta characters already have this.