I don't think it's right to draw comparisons to the PowerPC to Intel transition. I think that even though the two scenarios bear similarities, it's a pretty different situation this time around.
In 2005, PowerPC was a niche architecture for personal computers outside of Apple, and the most powerful processor was the G5, which didn't perform all that well and wasn't even suitable for laptops due to thermals. It was the final nail in the coffin since Apple literally had no suitable processor on the roadmap for many of its products. Even though many claim that the PowerPC architecture has untapped potential and is much more powerful than x86 in many respects, it simply didn't translate to real-world performance. (Even though it would continue to live on in products like the PS3, many manufacturers would later abandon it for similar reasons.) Apple was truly in a position where their top-of-the-line, newest PowerMacs were destined for obsolesce in a short timeframe as Intel Core processors dominated the market and x86 performance continued steadily adhering to Moore's Law through the mid 2000's.
Today is a very different situation. Apple is starting off on an industry-standard architecture of x86. Like many other vendors, they are upset with Intel over delays in product roadmaps and postponed promises of smaller die sizes. When it comes to the high-end of computing where thermals and power consumption aren't a concern, Intel is actually in a fine position still, even though AMD has pulled ahead. Regardless of whether it's Intel or AMD silicon, x86 is no longer adhering to Moore's Law, but on the flip side, most operating system software also hasn't really become too much more demanding at the CPU level over the last decade, so Moore's Law has had decreased visibility and focus. Graphics processing is now the focus. For laptops and low-power devices, Intel is starting to fall pretty far behind, however, both at the CPU and GPU compute side of things. This time around, it's not a matter of Apple not having any option for the roadmap of future laptops, it's a matter of things not moving fast enough to their liking, especially for portables.
I think it would not be outside the realm of possibility to really get 5-7 years of updates for Intel machines this time around versus the barely 2 years of support PowerPC got. Apple is coming from an architecture that's still very strong and still has vitality to it, but it's just not moving as fast as they'd like when thinking ahead for the next decade, especially for portables. And it remains to be seen if Apple silicon will ever be a match for something like an Radeon 5700XT or other high end graphics that prosumers need, but it probably won't be any time soon if ever, as annual discrete GPU performance boosts are now the new Moore's Law. The Intel Mac Pro, Apple's expensive and customizable desktop tower, will effectively keep x86 alive for the "years to come."