The SCT Inst scheme and the underlying market infrastructure are subject to Eurosystem oversight, and settlement takes place in central bank money. By contrast, so-called virtual currency schemes such as bitcoin, which have been 2/3  BIS central bankers' speeches  touted by some as the payment method of the future, cannot achieve that.
First, bitcoin is not a currency but simply a speculative digital asset. It tends to be processed inefficiently and – by comparison with instant payments – 30 times more slowly, and is about 10,000 times more expensive. The inefficient processing makes transactions costly not just from a financial perspective, but also in terms of the environmental impact.