Never will be: centralized,
False.
While unknowable a priori, that is quite unlikely.
False.
Well, you're batting zero for three in your stated criteria. So... ::bzzzt!:: wrong! It's the most Bitcoiniest of the Bitcoins. At least from the standpoint of the design of the protocol itself. The only legitimate claim BTC/Segwit/Core has on the title is popularity. Which can be fleeting.
Few mining pools, few nodes and less and less. It's centralizing, that's a fact.
Average Joe won't spend 1600usd (HDDs only) to run a full node
As long as there are no structural barriers for new entrants to the space of non-mining, fully-validating clients (i.e., what you so blithely mis-refer to as 'full nodes'), the network is exactly as decentralized as it need be. It's not as if having lots of non-mining, fully-validating clients actually provides any benefit to the network at large.
As far as mining:
# of pools required to make over 50% on BTC today: 3 - BTC.com 28.47%, F2Pool 13.19%, Poolin 11.81%
# of pools required to make over 50% on BSV today: 5 - Coingeek 27.08%, Mempool 11.81%, SVPool 6.25%, Dpool 4.17%, BMG Pool 3.47%
So... ::bzzzt!:: wrong! Again.