If something is heavy, too heavy or not, this is really subjective and individually. Where is the border?
Impo, dev does well at the moment (and in close future afaik). Anyway, its great already, and it will be (more or less) greater in future.
A lot of things are subjective, but there is a general consensus for what most people define as light or heavy bondage (you have already done the distinction yourself pretty well in some earlier comments). The latter having more chances to scare off potential players that may be interested in your game.
Regardless, the idea to make such polirizing contents optional remains, in my personal opinion, the best approach. But from a dev point standpoint, I also imagine it's not very motivating to work on something that may be played only be a really small portion of your playerbase. It's perfectly understandable.
Hence my comment. It's always a good thing to share your opinion because the larger the sample, the easier it is for the dev(s) but it's also important to be realistic and not expect too much either.
The game in its current stance is quite enjoyable and I look forward to the updates regardless of what they bring. I just don't want to get my hopes up in that particular aspect because I often find myself disappointed and I found the precautious option to be more pleasing overall. Take games for what they have to offer and if there is a bonus content that features a special kink of yours, its just the icing on the cake.