Thank you everyone for your reply. I guess the larger ThinkTank Bag ($250 value) has thus been retired as a gift for Platinum membership, as most of what I could find for the last year or so online has been pointing to the ThinkTank Laptop Bag.
So when I called CPS to inquire, they would not tell me what the gift was. However, this is what I did find out:
"Welcome" Gifts are only for new members, but you are considered qualified for welcome gifts as you upgrade between levels. You will not receive addition gifts upon membership renewal. CPS Straps and Lens caps are given for gold and platinum membership subscriptions and are considered welcome gifts. He hinted that they may offer a CPS online site for purchasing accessories in the future, because many members inquire about how they can obtain more straps or caps - I get it, it's a status thing.
Chose wisely young Padawan. If you qualify for gold today and upgrade your silver membership to gold, and a few months down the line you qualify for platinum and you upgrade then, you will not get any pro-rated price, you will have to purchase full price upgrade. Also applies if you are qualified for Platinum and decided to initially only purchase gold but then decided you wanted to upgrade to the higher membership. It's disappointing they don't allow you to simply pay the difference when renewing to a higher level within your membership timeframe, but if you wait until your renewal and upgrade then, it's all good. The CPS Rep mentioned that there might be an exception if you bought gold and decided after a few days or a couple weeks to upgrade to platinum, but that would be the exception not the normal practice. He recommended getting the membership you really need/want at the time of purchase.
The cost of body maintenance alone is $140 per incident. For the price of gold membership ($100) it's worth owning it even if you only service one piece of gear a year.
Gold membership is $100 and includes 5 service maintenance incidents for body or lens. Turn around time is 3 days (upon receipt). It also includes 20% discount on repair service. Equipment evaluation is available, but a 2-week prior window is required at a minimum. Loaner equipment is available upon receipt of an item that is sent in, e.g. if you require a loaner, they will only send it to you once they have received your gear.
Platinum comes with free shipping both ways; has a 2 day turn around time (upon receipt), a 30% discount on service repairs, maintenance for 10 incidents, priority on evaluation equipment (no lead time and you get priority over lower level members). Loaner equipment is available once a maintenance incident is initiated, e.g. when you schedule your gear to be maintained or repaired, they will send you a loan even before receiving your gear.
The Think Tank Artificial Intelligence 15 V3.0 bag is worth approximately $55 on Amazon, so not nearly the value of the previous Think Tank welcome gift, but at $300 for a Platinum membership now vs $500, we can assume that extra $200 paid for the full DSLR bag on the old Platinum plan.
Thanks everyone again for 2015 Platinum gift feedback, hopefully when I'm ready to upgrade to Platinum, Canon will be able to offer a more substantial gift. I hope members of this forum will continue to post new welcome gifts or tips about CPS memberships here.