We can borrow some ideas from ArcGIS topology editing feature.
Here are a lot of interesting PDF related to ArcGIS: 2007 ESRI International User Conference.
An interesting one is:
Also it looks like ArcGIS defines Topology as a separate entity which means relation between different Feature classes, I guess something similar is defined in OGC standards, but probably too abstract. Of course we should re-implement ArcGIS but some ideas can be used for our implementation based on SharpMap.
