I think that the routing max lenght should continue as it it's and the execution speed should be the same at all levels, in the end there is people who whould like the create really comples AI, also creating a limit on the AI routine max lenght or changing the execution speed on longer routines will cause people to just create attack only then harvest the resources routines, whereas creating longer routines will allow for more complex solutions, also having the new bots will add much more juice to the routines people will want to create.
I dont know maybe a sniper bot, you might want to create a long routine to scan for enemies carrying resourses and snipe them and only move while no enemies exist or contemplate enemy shield/hp for selecting a tarjet based if an ally is nerby.
There are so many possibilities. I would feel sad If a execution slowdown comes into play although in the end we will find a workaround for that, not sure what the intention is in adding such a feature.