Interesting and thanks, Jaenks, for reporting this.
Frankly, if this is confirmed to be true, then I will not make any effort extending my E+ status. The vouchers were the main benefit of E+. If I use the vouchers, I want to have certainty that I will be sitting in J. Unacceptable if TK now expects their top-tier customers to use the voucher but wait until boarding (yes, I am exaggerating) to find out if they are sitting in Economy or Business. I will not use the vouchers if there is any risk of ending up in Eco...
Combine this "voucher situation" with the "low cost carrier style of catering" and there isnt much to attract me to TK for the time being...