@do7d - I've never played with the extended map overlays. Interestingly, I was reading all about them during my 3.7.6 update work and thought "wow, I could do some really cool stuff with this". However, it is a matter of time and putting food on the table.
People that are buying customization services always get top billing. When I finish their requests I go back to routine development, patches, updates. Luckily I've had a LOT of those requests lately, which means my family is not eating mac & cheese every day. The downside is working on cool new features, even the ones I WANT for my own selfish reasons for my "SLP based web service" get put on the back burner.
If you have the skills to do some PHP coding the hooks & filters provided in SLP 3.7.7 (and earlier) allow you to do a TON of modifications without having to change the code. You may want to look there. If you don't see what you need let me know and I may be able to get it in a future update.