I think radical these days anything which goes against the tenets of neoliberalism and open markets - because they've been hegemonic for about thirty years now.
So challenging that system would mean challenging the 'existing legal frameworks' that support it. Yes, some people on the radical left have tried to challenge it within existing frameworks - like Syriza in Greece and Sanders in America - but they have failed.
What is interesting though is that the people considered radical at the moment are not on the far left, but the far right. European nationalists like Farage, Le Pen and Wilders are considered insurgents against global capitalism, as is Donald Trump. But curiously when you look at their economic policies you see that they really represent a new species of neoliberalism. Donald Trump's cabinet is made up of corporatists, hedge fund managers and investment bankers. I think one appointee is this hedge fund guy who has made billions from the same failing steel industry that Trump is supposed to be saving. Of course the rust belt people he claims to represent are just going to get screwed over even more.
Imo, what has happened is that capitalism is fucking up - or at least the market capitalism that we've had in the West for the past three hundred years. And while the populist right have got a radical response to this (blame migrants, Muslims, cuddle up to Putin and Assad and make lots of offensive comments about groups favoured by liberals, basically), the left are stumped. They have no idea what kind of system to argue for in its place.
So while I think Corbyn and people are right to put forward these quite radical and much needed policies (like a wage cap, for a universal living wage), they are not coming up with policies which address core problems like automation. We cannot go back to the kind of mixed economies with full employment that existed in the post-war era. The left need to think of something else.
So I would say no one much is being particularly radical on the left at the moment. Everyone is just fumbling around, not quite sure what to do while the world goes wrong, and proposing policies which are essentially sticking plasters rather than structural correctives.
Worryingly the only people who do have a radical agenda with electoral viability are crypto-fascists. This could be the beginning of another fascist Europe. Or it could be the start of a new form of social democracy. Who knows.