Having to keep it simple is nothing new on these schemes. When the DC Lines was done in 1988 it was the early days of SSI and the interlocking capacity was crammed to the hilt, not so much in terms of the actual number of modules but in the amount of data required against the available processing capacity. It's quite easy to add 50% to the cost of a resignalling or remodelling scheme by putting in stuff which will only be of significant benefit on a couple of days in a year. The rest of the time they can be a real PITA.
Eric's Square Law of Scheme Development Mistakes theorises that the probability of causing a c**k-up is proportional to the square of the options available -1. Put simply, only give one way of how to deal with something, 1 squared -1=0. 2 options, 2 squared -1=3. Give 3 or more options and you are deep in it.