There's a lot that can be done to separate and optimize various elements of a Magento 1 instance. At JetRails, we commonly separate out the frontend, database, admin, caching, and site search into separate servers (whether bare-metal or cloud). We also have some customers that are leveraging PWA frontends with Magento 1. This is not a full micro-services architecture since Magento 1 is not built to with the API driven backbone that a true microservice platform would require, but it can still have a big impact on site optimization, especially when paired with the right CDN and other resources.
Given that Magento 1 wasn't built with a micro-services architecture in mind, and it's about to reach its end of life if you want to truly move forward with a microservices architecture, I'd suggest it would be better to invest into Magento 2.