The transition will be probably smooth and transparent for business and consumers. Banks are already deploying payment terminal able to handle both Bizum and VISA/Mastercard [1]. Since banks own these terminals, they can decide how fast they want Bizum adoption to spread. Business don't even need to opt-in into it. At some point they can simply start charging for credit/debit cards and people will naturally switch to Bizum.

[1] https://www.bbva.com/es/es/empresas/bbva-primer-banco-en-esp...