My main concern is that gradle might not work as well as M2E in Eclipse which makes incremental compiling blazing fast (less than 1 sec for editing and compiling)

Gradle (as Buildship) is a top level supported project in Eclipse.

https://github.com/eclipse/buildship

you will be pleasantly surprised.

https://www.vogella.com/tutorials/EclipseGradle/article.html

But more importantly, i do request you would create a single source repo. your private dependency system is bit hard to work with. Even if you use mvn

Thanks! As long as maven works for you, just stick to it.

I'm also happy that it is plain Java as it means I can contribute without learning IntelliJ or anything special.

Thanks for willing to contribute. I will write some guideline for that later. Also it is possible to develop in IntelliJ, just that you need to run "mvn compile" from command line every time you changes the dependencies. While in Eclipse, it is fully automated with help of M2E.

No worries. For some reason I personally prefer NetBeans and Eclipse to IntelliJ, that's why I appreciate that you stick with plain Java and Maven instead of Kotlin and Gradle :-)

gradle works on commandline. Gradle has nothing to do with intellij.

Gradle supports modular building and other cool things that improves productivity. And a gradle build file is like 1/10th of a POM.XML file. Try it sometime.

I didn't say that Gradle demanded IntelliJ.

What I meant was that if author had switched to Kotlin it would have been hard to contribute without IntelliJ.