System76 is reportedly very close to being able to offer Coreboot on their laptops, and Tuxedo Computers and Slimbook both recently announced that they are now working on Coreboot as well, so in a year or two you should have a number of options besides Purism.
I think it likely that the next generation of Librem 13/15 will have a 4C/8T CPU, due to the fact that the 4-core U-series of Kaby Lake-R has a 15W TDP, just like the i7-7500U did, and Purism usually offers a high-end CPU in that 15W TDP. However, it is highly unlikely that Purism will offer an H-series CPU with 6 cores, because the 45W TDP would mean a substantial change to its laptop design.
One of the issues is that Purism sees its core mission as offering privacy, security and software freedom in a convenient package that the average person can use, which is why it focuses on creating slim and light notebooks, not workstations. Todd Weaver says that he started the company so that he could give electronic devices to his two daughters without worrying about their privacy. The focus is on promoting user digital rights, by giving the average user a convenient way to protect their digital rights.
Another issue is that Purism creates its own custom motherboards and cases, whereas the other Linux companies (System76, ThinkPenguin, Tuxedo Computers, Slimbook, Station-X) order base models from Clevo, so they can offer several different models including workstations, whereas Purism has to sell enough units to justify custom manufacturing, which is why it only has one line of laptop.
A third issue is the fact that Purism has to do Coreboot migration for each new generation of CPUs, so it is always going to be farther behind the tech curve with older CPUs, because it takes a while to update Coreboot for the latest CPUs.
A fourth issue is that Purism is likely to focus its future engineering on projects where it can offer 100% free software and a free hardware motherboard and case. I predict that its next project will be an i.MX 8M Quad tablet or a i.MX 8 QuadMax laptop.
Hopefully, it will eventually become a big enough company that it can start offering a workstation line of x86 laptops.