There's logic in these arguments; however, they ignore securities laws.
If BTC is a security, which the regulators probably think it is, then yes—you have to have a mechanism to bring concepts like splits, tenders, dividends to holders of the security if you are going to hold them for their benefit.
Developers considering forks will likely be required to follow yet unclarified rules around how much, how often, waiting and disclosure periods, etc.
(It's useful to consider how rules and systems have evolved governing how often Apple can split its stock or how Facebook investors are notified about tender offers, etc.)
The funny thing is that Bitcoin, because of its decentralized nature, doesn't have an entity tied to it (like Apple and AAPL). So who has the authority to "split" bitcoin? To "spin off" bitcoin? And under what obligation are the exchanges required to accept those modifications/additions to bitcoin?
It's more like I announce tomorrow that I am going to issue a Pear stock at 1:1 for each existing AAPL stocker holder. Would Stock Brokers like Scottrade need to accept Pear stock on behalf of their customers that owns AAPL stock? Under what authority can I "spin off" an AAPL stock?
I don't think Coinbase is under any obligation to honor any Bitcoin spin-off/fork/split, unless it is done by an authority of bitcoin (like Apple and AAPL), which for decentralized crypto currency like bitcoin means no one.
If BTC is a security, which the regulators probably think it is, then yes—you have to have a mechanism to bring concepts like splits, tenders, dividends to holders of the security if you are going to hold them for their benefit.
Developers considering forks will likely be required to follow yet unclarified rules around how much, how often, waiting and disclosure periods, etc.
(It's useful to consider how rules and systems have evolved governing how often Apple can split its stock or how Facebook investors are notified about tender offers, etc.)