It's a strong indicator that they find the technology useful. I don't expect Swift is spending shitloads on blockchain solutions just to bump their stock price, because they are a Society and don't even have a listed stock + probably they would be the first to debunk the blockchain tech if it was indeed useless (as it's a direct competition to their service). Just as I find it hard to believe that Blockstream would manage to sell their private blockchain solutions to any business if it was indeed inferior to the existing tech etc.
You did read my previous post? SWIFT actually agrees with the author that blockchain in its current state is NOT suitable for payment systems (which is no surprise given the current 14 tx/sec limit for bitcoin for example). Maybe some day someone will invent a new algo and it will work. But who knows if that's even possible. Until that day bitcoins is worthless as a payment system.