If each volume is going to be 300-odd pages, hardback might be unlikely.
Can't speak to the Treasury's decision-making, but my POV would be that The Trigan Empire has been a bit of a niche purchase (a dozen 100-odd-page books at around £45-50 a pop) and while the quality of those releases has been very good, they have naturally had a very limited audience. That's also before you get into the question of the reach that a company like Rebellion has that a publisher like The Don Lawrence Collection doesn't. Ideally you want to serve the audience who were aware of the series but couldn't justify over £500 for a complete collection, as well as a wider audience who you're going to make aware of the series and are looking for an appealing price point (the niche audience who would buy a series of expensive deluxe hardbacks will likely already have done so, after all
)
The Charley's War paperback collections were around 300 pages each with a RRP of £20, so I would think something like this in a similar format with colour interiors would be a bit more (maybe £30 or so?) but still heading toward a more mass-market pricing. Going that route gets a classic British SF epic back out there in an appealing package and gives the Treasury a showcase release for as many volumes as they commit to (I think four would do the currently-available run from the Don Lawrence Collection, with another couple of volumes seeing the whole series out there).
