Just to be clear, the tagging would occur on the addresses, and the weighting would be by value, so it's a measure of economic significance. Major exchanges will regularly tag massive amounts of Bitcoins with their capabilities.
Just adding a nice bit-field and a tagging standard, and then charting it might be enough to "think about how to use it later". The only problem would be that this would interfere with "other uses of op_return" ... colored coins, etc.
Personally, I think that's OK, since the purpose is to tag economically meaningful nodes to the Bitcoin ecosystem and colored coins, by definition, only have value to "other ecosystems".
(Counterargument: Suppose in some future where this is used as an alternative to BIP9 for a user-coordinated code release - especially in situations where miners have rejected activation of a widely-regarded proposal. Suppose also, in that future, colored coin ICO's that use op-return are regularly used to float the shares of major corporation. It might be irresponsible to exclude them from coordinating protocol changes.)