Trog, land was bought by the rail companies between the wars for 4-tracking. We're still waiting.
Techniquest, Arena and Bermuda stations are under construction. The planned bay plat at Coventry will have to wait. There is no stock available to increase the frequency until electrification elsewhere releases stock. See previous posts on this thread.
According to Centro, only one building needs to be sacrificed to 4-track the bit they want to do. It's an office. They also say that the bridges are ready for 4 tracks at M42, Tile Hill and A46. At A45 there are 2 bridges. The one for the eastbound carriageway that was built when the road was dualled, is suitable for 4 tracks without rebuilding it. The other one is the original 1840's brick arch bridge that Solihull council want to replace. Centro is pressing them to make it span 4 tracks.
People often point to the extreme disruption during the West Coast upgrade in the noughties as evidence that 4-tracking is not on. But the problems with WCRM were due to working on live tracks with short possessions. Where new tracks were added, as in Trent Valley, the work went smoothly because it was offline.