Difficulty would have risen slower, but would have still been out of reach for most people at the same proportion as today. The GPU makers have not been creating graphics cards with the target audience of general processing and algorithm solving.
ASIC/FPGA mining hardware has zero innovative aspects than what you would have seen a decade ago. These are simply dedicated chips for solving Sha-256 algorithms. ASIC stands for "Application Specific Integrated Circuit" and could mean anything, although the cryptocurrency miners use this term very loosely. But for clarity, the bitcoin ones are ASIC for solving Sha-256 algorithm.
The industry has always been able to make dedicated chips, as you have dedicated chips for Mpeg-2 processing in video editing rigs, your digital camera has an ASIC for processing light very quickly. Whereas the CPU in your computer is for general processing, with the most R&D being to create faster and more efficient general processors for a variety of applications, instead of just one.
So to sum it up, with a profit motive the Sha-256 ASICs would have come out a decade ago because there has been little advance in technology needed to create them.
Sha-2 was created by the NSA in 2001, or at least published by the NSA in 2001.
It is not a feat of engineering to make a machine efficient at solving one algorithm.
Another difference between a decade ago and today is that crowdfunding over the internet by presales would have been less trusted. Making securing the capital more difficult to create and produce ASIC mining equipment.
It is also worth noting that bitcoin can be switched to another algorithm if a vulnerability is found in the current algorithm (sha-256). This would mean that a different kind of ASIC would have to be created.
Finally, the folly of fiat currency mismanagement was not as apparent a decade ago during a period of prosperity, so people may not have viewed acquiring bitcoin as a worthy endeavor.