I've been developing Magento sites for my clients with eCommerce businesses since 2008. I can't believe it's going to be the 13th year of Magento development in 2020.
Magento certainly has come a long way, and changed ownership a few times - as far as I recall, without having to look up Wikipedia, it started with Varien then was bought out by a private equity firm who then sold it to Adobe.
I really like what Adobe is doing with their Creative Cloud. I can't say I'm a heavy user and I'm forced to pay close to $100 AUD each month. They've done a good job with getting rid of pirate software - or do I just think that because I haven't pirated software in like 10 years? What will Adobe do with Magento?
As far as I can forecast, certain businesses will always need an open source solution like Magento because Shopify just don't seem to cut it when it comes to running a marketplace.
I did see a marketplace option - but the way the Shopify plugin ecosystem works is that it runs much like a separate app - very loosely coupled and often not very optimally in terms of speed. So when I saw the WebKul marketplace app for Shopify and its reviews, I saw a lot of complaints about the speed. Magento 1 and 2 handle marketplaces very well.
Stadium Goods was on Magento and they reached out to me about a year or two back. Nothing came out of that conversation - it turns out they were undergoing a massive acquisition deal. Hats off to them and the founders. *Quickly checks the internet* - Stadium Goods still seem to be on Magento. It would be pretty cool to get some work from them but yeah, the point is that stores like this with heavy, heavy customisations will always be better on Magento versus a SaaS solution where you don't really own the technology.
Tl;dr - so we're not going to see a massive market share of Magento 2 in 2020 unless Adobe come up with something amazing that's SaaS and better than Shopify. But we're always going to have Magento 1 and 2 around because there is just no better open source alternative. (Reaction Commerce was looking promising though but I haven't checked them out in a while).