So I have run into the need of a possible mod. This may or may not be possible, so bear with me as I explain this.
I work on, and have for the past 2 1/2 years, almost daily on a MAJOR Minecraft project known as MineTrek.
The name speaks for what it is. StarTrek in Minecraft. We fully replicate 1:1 scale models of Starships based off all the plans and blueprints we can find online. This server is home of the iconic Megabuild of the Enterprise D made by Halkun back in September of '10.
So yes, this build has taken us a long time. About 3 1/2 years now.
Because our ships are all pretty much 1:1 (or slightly larger because of the Minecraft 1m block limit), and accurate to the plans, some rooms sometimes need to connect. For example, we'll have a block with a pipe texture going from one deck directly up/down/sideways through the floor/wall. So sometimes, it can be a bit complicated to picture what it all looks like without the walls/floor in the way. Here is an example.
This is our new-and-improved computer core for the Enterprise D (the one in the video)
Now this is how it looks like if you're inside the ship
Basically because we're working 'indoors', its kind of cramped and you can't see everything for what it is.
So this is where my idea and you magnificent modders come in.
How about a mod... where once enabled, you can select specifically what blocks you want to see and which ones you don't in some sort of menu. Like Nodus had the capability to see only ore blocks.