MAME 0.227 release has unfortunately been delayed to December 2020.
The slipping of release dates is nothing new in software development; it can, and does, happen with some frequency, for a whole assortment of reasons. That said, with an aim towards increasing the transparency with which the MAME team operates, we have taken the unprecedented step of announcing it, and issuing a (hopefully) reasonable explanation as to why.
The simple, and non-technical, reason for this decision is that the overall stability of the codebase, after some major changes under the hood in order to rectify technical debt after the release of MAME 0.226, is not where we would like it to be. As with many projects, we have a boilerplate set of tests which are run on a regular basis. When any major change to the core codebase occurs, there is the chance for instability – for reasons which will be clear in the more technical description to follow, the change was downright guaranteed to cause issues, despite the overall benefits once these issues are rectified. The metrics that have come from those tests indicate that the rate at which we are burning through regressions is not such that we can be reasonably assured of having a stable build by the time that it is necessary to have one to maintain a monthly release cadence.
For more information, see: https://www.mamedev.org/?p=489#readmore