First off, I want to say that each developer might have his own opinion regarding certain matters that don't necessarily reflect the views of the entire team, or project. I don't want to throw anyone under the bus here, but I don't know why the case is being made that PlugY is incompatible because we intend SP players to play a certain way, when the sole and only reason PlugY doesn't work is because of the new engine.
There really isn't any need to discuss it any further. I repeat: PlugY is disabled because it doesn't work with the new engine. If we were against multi-stash, we wouldn't have shipped PlugY with the launcher in the past. Nor provide certain files inside the mod that would make certain stats (such as signets) display on PlugY pages.
Next: PlugY is a third party tool. It's not built-in in our project, so the few people claiming we are taking steps backwards, we never took that step in the first place. The new engine came with sacrifices, and PlugY/D2SE were some of them. If you're a SP player, I'm happy to note that you can make a choice to play the old version if the benefits of PlugY for you are greater than the new engine.
More: saying we are neglecting the SP playerbase is just idiotic imo. Not only do we try to make the solo experience more enjoyable by providing increased drops and increased exp rates (both which required engine efforts), but we also risk all our server code / engine by keeping the mod SP-playable. If we decided to disable SP, we could have all our server code safely from being stolen (it only took china about 1 day to launch their sigma ripoff) and we would be able to implement lots of cool server features. But we haven't, and we shipped the server logic in the SP patch because we acknowledge and appreciate our SP community.
Extra: the possibility is there of PlugY making a comeback, but you have to understand, this wouldn't be a smart thing to do on a first release, because we want the bug reports to be centered on our actual product before we provide support for 3rd party tools. In fact, some cool person in this community had a working PlugY in less than 24 hours of release. We are looking into this, as we have to consider how this would work out compatibility-wise whenever we decide to implement our own multi-stash system. You just have to be patient.
Bonus: there seems to be a lot of expectations coming from some players which apparently assume we released the update with everything we wanted, as we wanted it. That's just not the case. We released on the 18th primarily because we were very commited to having this patch out as promised to the community. But this also required sacrifices, as we were unable to provide all the features we had planned for the initial release, which we are working on now. We preferred to have people miss a few features early on (extra waypoints, bounties, etc) rather than continue to ask about when sigma will be out and play on a dead ladder.