Excellent questions. I've started my adventure with MTGO about week ago, and although I have no paper collection, I still could invest some money in a digital one. But yeah, MTGO looks like a relic... My biggest concerns are:
WOTC will shut down MTGO and will not give us an option to transfer our collection to a new product.
The new product will be somehow dumbed-down (like many products nowadays), game mechanics simplified etc.
The collection of cards in the new product may be somehow limited, and would never get as vast as in MTGO, because of WOTC decision.
In the new product, they would focus on a story (I don't care about story - I do care about mechanics, game depth, and endless deck-building choices), forcing me to play campaigns against AI, while all I need is a platform for duels with real people, as I am also well over 30, live in Poland, and I have no time to participate in any real-life events.
I remember that many years ago, when I was buying PS3, my friends were able to tell me what is the planned life cycle of it, so I knew is the investment worth it or not. I have no idea about MTGO though, and I wish I knew this.