Also would like to chime in here to provide some assurance/insight/recomendations. We try to take great care for making changes to phpbb's theme, there are different limits between the different release types that we put on our selves to achieve this.
We have three types of releases version/major/minor
3 - version release, no restrictions this is a full change in no way meant to be compatible with the previous version and rarely happens
3.2 - major release this has some restrictions placed on it to maintain backwards compatibility, but can be broken if a strong case can be made for it as is the case with the icons you referred to previously. happens every 1-2 years or 10 as is the case with 3.1
3.2.1 - minor version restrictions are hard set and cannot/should not be broken but we are only human and occasionally something that we did not catch makes it through which is where the style authors are usful so that we can try to fix it. happens frequently to combat bugs and what not.
given this lets look at a specific exp:
The icons were not implemented in a way that was recommended by industry standards or font-awsome themselves, did not allow for complete compatibility with screen readers, were not easy to use/ customize/edit on your part as a style developer or a board admin. There is a very lengthy discussion that took place on area51 where anyone can raise concerns: https://area51.phpbb.com/phpBB/viewtopi ... 7c#p284641
. The discussion then can continue on the tracker when the ticket is created: https://tracker.phpbb.com/browse/PHPBB3-12769
it did not in this case but anyone can also weigh in there. Lastly the discussion finally continues on the specific pull request on github: https://github.com/phpbb/phpbb/pull/3851
also where anyone can continue to raise concerns about the specific code changes themselves. Also the icons are going to change again in 3.3 because technology has shifted away from font based icons go figure we adopted a technology on its way out
. However we are looking at this to try and make it as easy a transition as possible. fontAwsome 5 will have a framework for converting the existing code to svg versions that may be a solution to avoid changing the code too much if at all which may be an option, but its too soon to tell.
As for your specific concern about quality styles and the specific style that you are referring to PBTech...This is a great style, but not related to anything that you pointed out. PBTechs original author left the project prior to the release of 3.2 and the project was picked up by another individual. This is why its not a 3.2 style, futher complicating its update is the fact that its 1 of several themes in a line of themes that was based on the same framework. The new author chose to completely re-write the themes to make it easier on him to manage them which happens when you switch authors as its hard to understand someone else's code, however in doing so the framework was removed making it somewhat slower to rapidly update the styles all at once requiring individual releases which is why it has not been ported yet. However he is working on it just give him time.
As for the original quote that started this discussion...you missed the point and some of the recommendations that was also in the same post I believe.
The issues is not just with us making changes but also the way in which the styles are made/used/updated/tweaked and they way the template inheritance system currently works which in my opinion is flawed somewhat.
You should not be using the default theme...ever!...even if you only intend to use prosilver or whatever the default theme is in the future. Never use the default theme. Always duplicate the theme and give it a custom name. Then create a new css file with the custom name and include it as the last file in stylesheets.css and place any and all changes/tweaks/new css in this file(you can use preprocessors if you like but have them all render to this file. This way when a release happens the only thing that needs to be looked at for making fixes is this one file that you control and organize(or your scss/less files) and any changes to the html files which are usually very minor unless a theme has a complete re-write of a prosilver component which will require a little more work but not much, 1-2 hours most likely.
This i how you future proof a theme. This way you only have to update specifically what we fixed and you can easily keep an updated version as changes to the next release get merged by following the repo on github.