I'm not so sure TomTom needs to worry. The move from standalone devices to smartphone navigation software effectively means a lot of people no longer really know what TomTom is, as they'll use Google Maps or Apple Maps. You CAN get TomTom for mobile, but it's probably not as widely known or respected as it was 3-4 years ago.
The main reason that TomTom for mobile is not so widely known is that it is what powers Maps on iOS and Mac OSX devices. You don't need it anymore because you've already got it!
I don't think TomTom was ever quite that ubiquitous that it risked becoming a general term. When stand alone navigation devices were popular there was always a healthy level of competition between different brands, and also a healthy sector of the market provided by the de-branded OEM devices.
The owners of Hoover have done a better job of protecting their trademark with respect to vacuum cleaners in Australia, where it has never been used as a general term for all vacuum cleaners. There's no risk of them losing it when it next comes up for renewal in 2018.
I expect that Google will face some organised opposition when Google® comes up for renewal here in 2019, and they are more than likely to see the scope of the trademark scaled back a little.