This seems to be the only viable option if you want some certainty of not being spied on through a hardware back door, rather than modern chips where you're pretty much a guest on some kind of mysterious hypervisor.
I wonder what the theoretical limits to performance and usability of a 74xxx computer is. Email and chat should be possible as they were on 74xxx machines in the past, maybe even Gopher-style web browsing. But it's a hard sell when everyone's hooked on HD or even 4K video streaming.
Yes...you could run CLI apps just fine on TTL machines. I have a DEC VAX-11/730, which is TTL+2901 Bit slice (so not all 7400) going at about 1/3 MIPS. Runs BSD 4.3 and is on ethernet, and I can develop software (C/C++), chat (IRC), gopher, games (nethack) and even HTML web (lynx). But crypto (TLS) is rough, and things like streaming media and modern web are right out. And it uses a couple of times more power than my dryer does...not very environmentally friendly.
But practically, the limits of a 74xx series in creating a 'modern feature' (like, 32-bit) CPU are manifold. Assuming DIP chips, it would pack an average of 4 logic gates in about 1 sq inch (hand-waving a bit, and including board space). A Cortex-M0 has approx 12,000 gates [1]. So it would be huge. Assuming LS logic, each chip would draw about 4.5mA peak, so about 13.5 amps peak. So it would use a lot of power. Propagation delay (maybe 10ns per gate in LS) means it will be much slower than integrated logic...perhaps a couple of orders of magnitude slower than an M0.
There are mitigations. You could use SMT packages and pack more on a board. You could use a more power-efficient logic family than LS (e.g. ALVT or some CMOS family). Or go for faster logic at the cost of power. But you're never going to get within an order of magnitude or 3 of the speed+efficiencies of a monolithic chip.
There are a number of homebrew TTL CPUs out there for comparison. Most are 4- or 8-bit.
Now I know how to market it! "You're not doing real microservices unless you do it on the gate level!"
But it's cool that you have a working VAX. I've been wanting some kind of minicomputer for a long time, but if I could find a complete one I probably couldn't justify the cost.
I guess any 74xx chip can contain an SoC running a complete OS, and in the case of RAM be able to read and write anything it wants and phone home about it. But it would be very conspicuous when a chip that should only contain a handful of transistors or a simple grid pattern of memory cells is decapped. They are far more auditable than anything VLSI.
It's true that the battle can't be won, but that means it's a war of attrition. Backdooring 74xx chips would be very inconvenient and expensive compared to just pushing some code into the Intel ME or AMD PSP. The flip side of that is that building and using a 74xx computer is going to be just as inconvenient and expensive for the user. So this is more of a fun thought experiment than a serious solution.
Actually more than one, and new projects are started everyday to RE more architectures as we gathertools and knowledge from previous efforts. While the newer higher end fpgas are still out of reach a Lattice ECP5 can do pciE, gigabit ethernet, hdmi, ddr3, usb3, and of course has more than enough for a RISC-V (as a matter of fact you can fo one in a much cheaper/smaller ice40: https://github.com/cliffordwolf/picorv32
If you're going down this route, an FPGA can have a whole opaque processor embedded in it (usually an ARM) that theoretically is doing things you don't know about.
I wonder what the theoretical limits to performance and usability of a 74xxx computer is. Email and chat should be possible as they were on 74xxx machines in the past, maybe even Gopher-style web browsing. But it's a hard sell when everyone's hooked on HD or even 4K video streaming.