I reckon ARC Pro is an excellent system. The Le Mans 24h set has everything you need to get started, although you will want to get a pitlane pretty soon to get the most out of the ARC app's pit stop features. The upgrade set just has the powerbase, power supply and two controllers - you'd also need to buy digital chip modules to put in your cars and a lane changer to change lanes. Plus that pit lane.
ARC Pro was released just before Christmas 2017 - so it's not that old! There were some necessary hardware revisions (although that is stable from 2018/9) and there was a brand new ARC app released in 2018, which has also had revisions and bug fixes since. There's the option of the more complex Magic ARC app, which gives a richer racing experience - this third-party app has also been developed and bugs fixed.
ARC Pro is an evolution of the original Scalextric digital system - they share essentially the same communication protocols, so the lane changers and digital decoders are compatible with powerbases from 2004/5 onwards. What ARC Pro added were the wireless controllers and a Bluetooth link to use a race management app on a phone or tablet. There's also a physical switch for a traditional 'analogue' mode. Apart from the Magic app, the third-party add-ons for ARC Pro have been thin on the ground - although it's possible to upgrade the controllers with a Slot.it SCP oXigen controller.
You might want to take a look at
this thread, which is about how you could develop the older C7042 Advanced Powerbase to give an arguably better system via a PC or laptop. If you are looking at running on your own against multiple pace cars, this is much more exciting option. If you're looking at an easy-to-use, great value system with wireless controllers, then ARC Pro is the one for you.
What's the future? Fans of the oXigen and Scorpius systems would say wireless control of the cars - essentially radio control with the cars getting only power (and steering) from the slot. I would probably agree - although I think most Scalextric (and Carrera) digital racers are more than satisfied with what they have. There was a similar shift in the model railway world from the traditional digital signal-via-the-track to radio control... However, from what I can see, the vast majority of enthusiasts have stuck with the traditional digital systems - and Hornby haven't gone down the radio-controlled track with their trains, yet... Despite the availability of oXigen and Scorpious for over a decade - and their advantages - it's the Carrera and Scalextric signal-in-track systems that are used by almost all digital slot car enthusiasts around the world.