Unfortunately, I think the fact that we already know who lives and who dies, and who ends up on the Iron Throne at the end, is going to take all the suspense and tension out of this new show. Imagine if, when GoT had first aired, it had already been common knowledge that Daenerys, Robb, Stannis, as well as most of the other Starks and Lannisters, would all die and that Bran would become king at the end. Even for someone who hadn’t read the books, there was no way they would’ve been able to avoid spoilers during all these years. GoT (and ASoIaF in general) wouldn’t have been half as fun without all the theories that people came up with over the years. But there won’t be any of these theories for House of the Dragon, because we already know all the major deaths, reveals and betrayals that will occur (at least in broad strokes).
The only way to get around that would’ve been either a prequel that takes place far enough in the past that we simply don’t have enough information about what happened, or a sequel that takes place after the events of GoT.
Or (and this option is a personal favorite of mine), they could‘ve done an alternate universe take of GOT, taking place in the same time period and with the same characters as the original series, but under radically different circumstances. For example, a series that takes place in a universe where Rhaegar defeated Robert during the rebellion, the Targaryens managed to keep the throne, and Jon and Daenerys would‘ve grown up as a prince and princess, alongside Rhaegar‘s other children and Viserys. The upsides of this would be that such a show would have most of the characters people are already familiar with (though with different actors of course), but within a completely different story. And unlike with House of the Dragon (or even GoT for the first five seasons), no one would have any idea what‘s going to happen. It would be a totally fresh experience for everyone, even book readers and ASoIaF nerds, since they wouldn’t know who lives, who dies, who betrays whom or who ends up on the throne at the end. No prequel show could ever match the hype for something like this.