Many moons ago the idea was brought up to have a cap on how many coins could be staked on individual secretnodes. This idea has also been discussed by Vitalik for ethereum 2.0
Why a cap might be good to have? It discourages extremely large stakes by increasing the complexity of running a large number of nodes.
Why a cap might not matter? As seen on networks such as dash stakeholders who are determined to stake a large number of coins will go through the trouble to do so and with a cap it may be harder to determine how centralized the network is.
What are enigmas current thoughts on the concept of a cap on collateral size for secretnodes and what are the reasons associated?