I've noticed that the World Socialist Party of India employ the concept of 'decadence':
"However, by the beginning of the 20th century, the situation reversed. Capitalism entered into its era of decadence. Decadence – because, from then onwards, the revolutionary situation (objective condition) remains ready but the revolution has not happened owing to immaturity of working class consciousness and organization (subjective condition). (https://www.worldsocialism.org/spgb/socialist-standard/2014/2010s/no-132...)"
Which I would normally associate with left communists.
So where do SPGB/WSM actually stand on this, considering SPGB member Edgar Hardcastle criticised the concept of 'decadence'?
"Capitalism did indeed change in 1914. As Professor E. H. Carr puts it, up to 1914: "Britain was the pre-eminent Great Power, and the directing centre of the worldwide capitalist economy." Now the industrial and military centres of power have shifted to New York, Moscow and Brussels; but this has not altered capitalism's economic laws or introduced a new "decadence". (https://www.worldsocialism.org/spgb/socialist-standard/1977/1970s/no-878...)"
The spgb has always held a simplified version of decadence theory in my opinion without using that terminology. I mentioned this before in my brief comments #43 and #52 in the 'Confusion about decadence theory' thread. There is some discussion between the spgb and IP in the old IP archives site but I can't just lay my hands on it now. The spgb Indian group did of course have some previous discussion with left communist groups in the UK. before throwing their lot in with the WSM/spgb.
PS; as an aside the new IP website looks better but is worse than the old one if you are trying to find individual articles, including past texts that I and others have linked in libcom discussion threads. I've tried to raise this with IP but no change so far.