I like the idea.
I like the idea.
Communication. And grace.
If you're not sure if something is welcome, ask... politely. If someone does something unwelcome, say something... politely. If you see two other people involved in an unwelcome exchange, try to smooth the situation over while teaching lessons... politely.
I volunteer with a variety of alternative groups. It's actually logically impossible to act in a way that everyone's norms around touch are satisfied, because many are mutually exclusive.
In an absence of clarity, all we have is communication, consent, and fundamental decency in how we treat each other when one or both of us &#+@s up. Because we all will, at one point or another.
Teaching children to reach for polite assertiveness when called for, and polite apology when due, would go a long way towards making the world a better place.
(And just to head off the inevitable: we're clearly talking about sub-criminal actions here)
If you know for sure someone welcomes contact from you, then sure go ahead.
Otherwise, you're asking double from the person whose boundaries were violated: First, the discomfort of the unsolicited contact. Then, second, the discomfort of causing a scene to assert their boundaries.
It's nearly always easier to just accept the first small and incidental discomfort and move on - but it doesn't mean it was okay.
Examples could be a relative that criticizes your physique (e.g. a comment of the belly someone developed over the christmas holidays), mansplaining or a repeatedly interrupting colleague. Any sort of interaction bears the risk of violating someones boundaries (that one does not know because how could one if they didn't communicate them [0]). Assertiveness means that someone both knows where their own boundaries are, so that they actually can tell when they are violated and additionally that they have the skills to deal with it. This can be as easy as challenging the other with a "Oh? Do you think so?", making clear that there is something one does not agree with and that this is a topic the other would not have an easy time to pursue further. Assertiveness is not about making a scene, it is about clearly communicating that there is a topic that will lead to conflict if pursued further.
Basically it is a tool to make people stronger and more confident so that they do not become victims of other people's transgressions as easily.
[0] This does not mean that people shouldn't be somewhat considerate but being overly considerate is nothing more than social self-censorship. Others have to accept your personality as much as you have to accept theirs. It's an interplay.
Edit: This nice line is from Wikipedia: Assertiveness is the quality of being self-assured and confident without being aggressive.