I know the architecture too good, more than I need as I was leaving MS recently. This tweet is not likely to happen. Talking about desktop apps, this doesn't make any sense. Office apps have millions of lines in code and many years of lost knowledge between the classes. Just too many screens, checkboxes and features. A complete bloatware. Buy MS doesn't take any feature off the app- if you have 1B users, most likely that any minor feature cut will hurt some of them, hundred of thousand of them, and they are probably paying, not free riders. Any new office version only hides features, letting this small users group to get them back, never deleting lines of code. MS doesn't want to get billions fined as happend when they moved to docx/pptx/xlsx and didn't support backwards.

Talking about the online versions of office, it is a mess. For Word and PPT they tried to replicate the desktop to the web, rewriting the code, so their current online versions are already using (mostly) new code dedicated for the web. Saying that, they also have a huge number of legacy components and features that they need to support for backward compatibility.So for word and ppt this is a mix in code, not a total re-write. They also have a substantial subset of the features that appear only in their older desktop brothers. Even the PMs don't dare to dream on features parity between the versions.

Excel is a different world and a big-big elephant that won't likely be rewritten any years soon. Think of a code that is maintained over 30 years. Literally, developers are still maintaining code written in the 90s. Trying to bring Excel to the online world made MS create an architecture of html frontend which communicates with a dll session behind the scenes. As weird as it sounds, this dll lives as long as the browser has the spreadsheet opened. Think of it as MS raising VM for every excel file that is opened over the internet. While this is not very cost effective (saying the least) and not very performance friendly (hey ma! I made an understatement) this allowed them to move forward with Excel online very quickly by having a UI communicating with the bloatware dll that runs on the background in Azure. Summarizing Excel, it probably won't also be rewritten in js.

So this PM might be talking about the new apps - Teams or flow or something similar. Not the office cash cows. Personally I really hope he is talking about Skype which became a total garbage in the past versions.

Anyone from Google here? I'm looking for a job :-) ping me (chengmau) in the blind app