I think this is better left as a scenario specific rule rather than a core or optional rule.
A Lasalle base is around 30m wide. I doubt if there were any bridges that wide in this period. So even if you have a single column of bases going over the bridge it is a significant abstraction of what is happening in terms of fighting frontage.
The accounts I have read of attacks over bridges seem to have specific features unique to the circumstances. This is better catered for by having scenario specific rules that reflect what you want to have happen in that setting rather a generic bridge rule that may not be appropriate for the circumstances being modelled.
In an AB game the time frame being represented i.e. around 2 hours is quite likely not sufficient for the preparation and build up that surrounded bridge assaults, to take place.
Having said all that I did quite like the original suggestions and I am sure I will play around with some adaptations of them for my own games.
The only bridge crossing home rules I have tried so far was to give the defenders a no go zone on their side of the bridge which gave the attacker sufficient space to cross the bridge in march column and then deploy and then fight with normal rules from there. The defender still has a massive advantage as he can concentrate several units against one so the storming unit is quite likely to get destroyed.