This has become an exercise in pedantics. People are suggesting that PS4 demand is definitively declining, that this should be concerning to Sony, worthy of significant reaction, and launching a new console is the reasonable response to this.
First, I think it's naive to think that Sony isn't acutely aware of what their sales trends look like, or that they are uncomfortable with where they sit on the cost-demand curve, and finally, that they have no mobility on this curve while maintaining profitibality. They're still competitive with the market and have a slew of great titles lined up.
Thus, I don't think they're under pressure to launch the PS5, but rather, just not be beaten to market by Microsoft. I think that is unlikely to happen given the likely similar architecture between the two.
I think they should be careful of first party PS4 titles launching close to, or even after, the PS5 given we don't know how this will affect title sales and console sales, given it's a little unprecedented. Additionally, as seamless as the compatibility is supposed to be, it may place extra burden on the developers to support both consoles from launch. We know third parties struggled with this in the prior gen launch. I'm also a little extra sympathetic to first party devs since they're completely at the mercy of their owners to provide a market, console, and marketing.
I wouldn't automatically assume this. GloFo's first 7nm iteration is optimized for performance whereas TSMC is optimized for power efficiency. The latter is going for all the mobile whiles, while GloFo probably wants to make AMD APUs and GPUs.