It still kind of astounds me that they'd rip out a fully functional coaster that was only halfway into its service life for this. Don't get me wrong, Valkyria looks like an improvement on so many levels, it's just that the practice is so unheard of. It is very uncommon for a custom designed, running, popular coaster like Kanonen to be taken out that early in its life cycle and completely sold by the owners, because they consider the space better used for something else. Most parks build their coasters with the intention of letting them last for as long as possible, because the price has already been paid and their purpose is to give value back. They are usually kept standing for as long as they are profitable, and replacement only considered when it is practically the only option. When maintenance costs have risen and ridership sunk, that's when you consider scrapping a coaster. When it has gotten every last piece of profitability squeezed out of it, and running it costs more money than it gives back.
But Liseberg looked at Kanonen, determined it to have many good years left in it, and yet decided to remove it to redevelop the area. Only 11 years after it was built (okay, 12, since it served from the beginning of 2005 until the end of 2016), and without having a buyer ready (that we know of, it could be that somebody had made an agreement they pulled out of at the last minute). Since it costs money to dismantle the ride and to store it until a buyer can be found, the money made back from the sale can't possibly exceed the value left in the ride's lifespan (otherwise, who would buy it?). Liseberg essentially took a loss removing Kanonen, so that Valkyria could be built. That's practically unheard of, to me at least.
Right now, I can only think of one other example, in Big Bad Wolf at BGE. It too was popular when it was removed to make room for a new coaster, but at least it had served for 25 years by then. Its time had come and gone. The same could be said for Dragon Challenge, but it too had turned 18, operated year-round, and its duelling gimmick was put out of order. Other chains like Six Flags and Cedar Fair occasionally dismantle coasters and send them to other parks in the chain, but that means they keep the value of the ride internally in the company (minus dismantling/transport/rebuilding costs, of course). However, I can't think of any instances of parks removing relatively new coasters to make room like that without anything being seriously wrong with them. For comparison, Tatsu, Expedition Everest, El Toro and Stealth are all older now than Kanonen was at the time of its removal (the same will be true of Maverick in a few months), and I don't see any of them going any time soon. Can anybody else think of a park that got rid of one of their good rides while it was still not halfway through its life span, still popular, and still working just fine?
During the tour it was also mentioned that after Helix guests really didn't care for Kanonen that much as they found Helix to be a much better launch coaster than Kanonen was. The park also realized that it was a bit weird to have 2 very similar style coasters and decided to remove it.
The reason Valkyria is a dive coaster is because the park wanted a ride that focused on a big first drop as the others don't really do that (Balder kinda accomplishes that but it is quite small height wise).