The problem with including it by default is that we need someone to support it.
And it's better if that someone actually uses it so that it doesn't fall by the wayside. At this point, that someone would likely prefer to have its own release schedule depending on their need instead of being tied to the Nim team release schedule. In particular I expect people in extreme need of a decimal library are financial institutions that want to use it for accounting and accounting deadlines and Nim release targets are probably very different. Also I did work on AS400 computers supporting financial accounting applications written in COBOL, they already have a very hard time considering anything other than COBOL so I would be interested to know what are other users that would be interested in maintaining such a library. So it's not much a decision not to include it but the need of a long-term maintainer with some skin in the game (so that they don't disappear and dump the workload on the Nim team).
