Upgrades are always painful decisions. You have already invested thousands of dollars (if you are like me the investment was painful) and now you are asked to put some serious percentage of your original investment back into the product.
Well what I do is try to determine the benefit to expense ratio. Most of the time I don't update if I am happy with the product. Granted, a bit of upgraditis always exists but we have to be practical.
Companies usually don't profit much from upgrades (particularly owner installed. Owners make many mistakes, or don't read, etc.) So it is always a crap shoot for them. Really high end companies are not giants and any R&D time and planning spent on upgrades comes at the expense of other products.
If what I hear about this upgrade is correct, someone at the company saw a way to leverage newer technology into the Summit with minor work. Sounds good to me.
You Summit owners have a decision to make. If the price is too high, don't blame ML they have to make money and their prices are usually moderate considering the quality delivered.