Here's hoping that the horizontal version also becomes reality! I've been reading the T1 thread for a while now and almost made up my mind to purchase it as soon as it becomes available in large quantities. But now that I saw these designs, I may have to adjust my decision yet again! The T1 looks great, its design is on par with Streacom DA2 and Thor Mjolnir (not saying they look the same, though). But this one looks just so much better! Even though it might be cheaper than the T1, I'd gladly pay more for this one.
But I wouldn't buy a vertical version. It's just too dominating. I don't mind a bigger desk footprint. I only care that how much attention the case would get when I see it next to the display, and with the vertical it's just too much. Even though the profile area is equal, or at least nearly equal, the vertical case just perceivable looks larger and more attention-seeking. In addition to the - maybe irrational, but still - fear of toppling it and making it fall off my desk.
I also understand the people that disagree and who argue that there are so few vertical case designs available. It's true. But for me it just doesn't matter if T1 is available for horizontal builds, if the P1 isn't.
In addition, if the P1 is supporting 280 mm rads, I assume it makes the case 20 mm wider? I'm going to make an air-cooled build, so I really wouldn't mind getting that 20 mm headroom as well, as then I could have both the 70 mm CPU cooler height and 60 mm of room for the GPU. With the T1 I'd have to choose between using NH-L12S and a dual-slot card or NH-L9i and a three-slot card. Both are unoptimal, as the dual-slot cards are noisier, and the L9i just can't handle, e.g., a 10700K or even a 10600K. So I really hope the case is made to support the 140 mm headroom inside. Even the support for 50 mm GPUs when using 70 mm for the CPU cooler would make the life much easier, allowing to put in, for example, EVGA's 2.5-slot cards.
I'm waiting for the RTX 30x0 series in any case [pun not intended], so I'm not in a hurry to wait until, say, next January for the horizontal P1 to become reality.