I just called LifeMiles. The answer I was given was that we will still need to complete the 6 months of subscription for Club LifeMiles as required. There will be no rollover into the new plan. As far as subscribing for both LifeMiles+ and Club LifeMiles concurrently, it may be possible I was told.
Looks like we are stuck. I mean, I'm not upset. I bought the lowest CLM tier specifically because I had a bunch of upcoming bookings I needed to make and I liked the idea of making my 98,000 Capital One Venture X miles (90,000 sign-up bonus + 8,000 miles on $4,000 spend to get the SUB) go 10% further (so far I've transferred 48,500 miles. Without CLM that amount would have been an additional 9500 miles. All my flights on Avianca were similarly priced to other airlines (I have no brand loyalty), i.e. I wouldn't have purchased a ticket from AA or something for cheaper, meaning the $/mile value I got is what it is (as opposed to saying I got $0.02/mile from Avianca but AA or Delta at the time was $100 cheaper than Avianca), all of which has been great. The total savings value I've gotten from Club LifeMiles is $260.95 (If you want to do this calculation as well, find the original miles cost of the flight and calculate the $/mile based on the cost of the ticket less taxes that you paid. Then calculate the number of miles you saved because of Club LifeMiles. Then multiply the miles saved by the original $/mile value. You wouldn't want to use the $/mile value of the Club LifeMiles discounted price because you care about how much you saved versus no Club LifeMiles). On top of this they are giving me 6x600 miles, or 3600 miles. I'm averaging like $0.027/mile on these bookings (pre Club LifeMiles discount), so that 3600 miles is worth like $90+!
Edit: I spoke with another person at LifeMiles. He said that you would not get dual benefits, you would get the most restrictive benefits (that being Club LifeMiles). He recommended waiting until the 6 months of Club LifeMiles expires so that it can be canceled so as to receive the LifeMiles+ benefits. Of course, the waitlist bonus of 5000/10000 miles expires June 18. Strangely, though, you can go through the checkout process for LifeMiles+ (without the credit card, just buying the subscription outright) and it is behaving as expected, asking me to pay and telling me I have to subscribe for 6 months.
Edit #2: Interesting quirk in the terms & conditions for Club LifeMiles: "In case lifemiles is not able to charge the monthly amount to the member’s card, it will send one email to the member and will try to charge the amount three times every 7 days and the member will have 21 days to make the payment. In case it is not possible to charge the card, lifemiles will cancel the subscription and it will not be possible to reactivate it."
Edit #3: I talked to LifeMiles chat support via Twitter DM. This person said Club LifeMiles subscribers who get LifeMiles+ would get blended rewards since I'd be subscribed to both, namely any benefit that overlaps would be provided just once - meaning you aren't getting double 10% ticket discount since both programs offer it, you'd just get 10%. You aren't getting 2x miles twice, just once. The rep indicated we would get 1100 miles (600 Club LifeMiles Personal + 500 LifeMiles+ Lite) since we'd be subscribed to both programs. I am trying to figure out if the Free Cancellation/Changes benefit with the Basic plan would apply to existing tickets redeemed prior to subscribing. I'll report back.