Yeah 
If you compare the line art and the screenshot, you'll notice some rather obvious differences! The 418 is missing the ventral extension and the spinal trench, has a narrower central bridge, a bow antenna array and equal-sized gravity well projectors 
I just watched the Rebels episode, and I have to say I'm a little confused, for two reasons:
First, the ship seems way bigger than previous depictions of the Interdictor (by which I mean the 600m Vindicator-based 418 cruiser, not the fugly ISD variant). It's around 5-6 times longer than an Arquitens-class which, though its size has never been officially given, was believed to be in the 200-250m range and is definitely larger than a 150m CR90. This would place it in the 900-1200m range, i.e. 150-200% of the 418's given size.
The shape is also somewhat different, with a distinctive trench along its spine and an angular bulge on its underside. Though I suppose those features could be ascribed to artistic license like the giraffey ISDs, or indicative of a test prototype, which would be consistent with the show.
It's entirely possible that FFG release this version of the Interdictor - as a Medium or Large ship, halfway between a VSD and an ISD.
What is the 200-250 meter estimate for the Arquitens based off of? Because I rewatched the Clone Wars episode the Arquitens first appeared in and from comparing its size to that of the Consulars it was in formation with I would say it was around 150 meters long, maybe 175.
I'm not sure where it originally came from. It used to be mentioned in Wookieepedia, though it has since been removed. In any case it's clearly shown to be bigger than the CR90 in at least a couple of Rebels episodes. And even if it were 150-175m, that would still put the new Interdictor at 800m or more.
Isn't it a prototype though? Prototypes usually have different specs than the final production model and especially in scifi are usually bigger and more powerful versions.
Obviously this is the canonized version of the Immobilizer 418. Still odd that it goes by that designation in Tarkin but not here. I can not see why LFL won't eventually allow the designs to be one and the same, since the Rebels version is so remarkably similar to the Legends 418. The only differences can be chalked up to styling... like comparing ANH's Devastator to the Giraffe-type Star Destroyers, even though both of them are supposed to be Imperial-Is.
I'm still interested to hear/read what Interdictors are supposed to do. Splendid for you, now there's a new heavy-medium ship in the Imperial navy which does...what on the battlefield? Apart from making you wonder if your VSDs are obsolete again, I mean. Otherwise don't waste an Imperial slot by some objective-only dingus and give us something the Empire really needs... like a decent stand-and-fight small ship escort for the Empire that has some red and blue dice. I'm thinking of the Neb B-2.
I'm still interested to hear/read what Interdictors are supposed to do. Splendid for you, now there's a new heavy-medium ship in the Imperial navy which does...what on the battlefield? Apart from making you wonder if your VSDs are obsolete again, I mean. Otherwise don't waste an Imperial slot by some objective-only dingus and give us something the Empire really needs... like a decent stand-and-fight small ship escort for the Empire that has some red and blue dice. I'm thinking of the Neb B-2.
It's a light or medium cruiser that sacrifices firepower and squadron space to house massive gravity well generators. For Armada it would be (imho) the perfect Imperial ship for some fleet support abilities. We have enough pew-pew ships.
I'm still interested to hear/read what Interdictors are supposed to do. Splendid for you, now there's a new heavy-medium ship in the Imperial navy which does...what on the battlefield? Apart from making you wonder if your VSDs are obsolete again, I mean. Otherwise don't waste an Imperial slot by some objective-only dingus and give us something the Empire really needs... like a decent stand-and-fight small ship escort for the Empire that has some red and blue dice. I'm thinking of the Neb B-2.
It's a light or medium cruiser that sacrifices firepower and squadron space to house massive gravity well generators. For Armada it would be (imho) the perfect Imperial ship for some fleet support abilities. We have enough pew-pew ships.
We can never have enough pew-pew ships.