I seem to have managed to free myself a bit of time, which means I can work a bit on EclipseFP 2.6. I've added support for cabal sandboxes, so you'll be able to use sandboxing with cabal 1.18 in pretty much the same way cabal-dev was supported. You can have a per project or per workspace sandbox, and the fact that add-source is dynamic simplifies the internal code somehow. Cabal-dev is still supported.
A nice side effect of supporting Cabal 1.18 (thanks again to dynamic-cabal) is that we can use a sandbox to install the executables we need, like buildwrapper and scion-browser. Up to now, if you hadn't installed them, you'd get a dialog box asking you if you wanted to. Users have complained that this was an unnecessary step, but I didn't want to install executables with many dependencies into the user's package database without a notice. Now, executables get installed into a specific sandbox, so the install may be a bit longer if you already had some dependencies, but we don't mess up anything on your system.
The only issue is that inside a cabal sandbox, all packages need to be coherent: you cannot have two different versions of the same library. This shouldn't normally be an issue, but it is at the moment, because we try to install HLint and SourceGraph, that both require a different version of haskell-src-exts. I have sent a patch to Ivan Lazar Miljenovic so that SourceGraph can support the latest version of haskell-src-exts so hopefully this will be sorted by the time EclipseFP 2.6 hit the metaphorical shelves.
So hopefully EclipseFP 2.6 will be easier to install and will take advantage of the latest Cabal functionality!