For the sake of discussion, assuming Anaplan did increase the number of dimensions you can nest along the row or columns, the question i would pose to you is: should you as the model builder/solution architect suggest/build such a module, i.e. a module using > 5 lists (this is technically a separate but relevant issue).
Please remember the first guideline in Planual, i.e.
Besides the most obvious implication of increasing workspace exponentially, it also has the following downside to building a huge module:
1. It's difficult for user to select the right combination of list member to arrive at the desired combination,
2. It's difficult for model builder to write formulas that cater for all scenarios and list combinations.
3. Performance would suffer because you're likely to turn on Summary for some of the line items (i'm imagining you're requesting for a multi nested row/column because this module is an Output type module, and end users likely want to see aggregation of some sort).
Having said the above, as mentioned by @Misbah this >3 nested row/column option is not available at the moment, so please upvote the relevant ideas exchange post.
The output module can be any number of dimensions but in this case I combined two of them so I could nest them on the row pivot, essentially giving me the effectiveness of four dimensions but only having to use 3 (max).
Make sure to read @LipChean_Soh commentary on best practices (above) and @Misbah post as well. These are important points I didn't mention. To be honest, I kind of like the 3 dimension limit because it forces me to break up the process into manageable pieces and helps with user adoption. Unlike Excel where you have unlimited space to work with, Anaplan does force you to use a narrow amount of real estate so the steps have to be simple.
Then again, sometimes, you just need all those dimensions. We all face that challenge.
Great question and discussion. I hope you'll let us know what you decided to do.