It's too late. The genie is out of the bottle. Hinduism has never been a united or unitary religion. Due to the democratic nature of the religion to encourage freedom of thought, it has always been producing new thoughts and religions like Shaivism, Vaishnavism, Buddism, Jainism, Sikhism. Even the recent followers of Sai baba do not consider themselves as Hindus and only go to sai baba temples.
There was only one instance where the genie was put back into the bottle by Adi Sankhara when he brought back people following Shaivism, Vaishnavism, Buddism (majority) back into the fold of modern form of Hinduism.
That is ridiculous, pretty much all Sai baba followers call themselves Hindus unless of-course they are muslims.
Sikhism of Guru Nanak itself was a offshoot of Vishnavism which later on added Shiva, Vishnu, the Sun, goddess Durga, and Ganesh worship.
Guru Nanak's own son Srichandra was a Naga Sadhu and he founded the Udasin sanyasi. A divergence into Shiva worship.
This is the picture on the Front of the ORIGINAL Sikh Holy Book, Guru Granth Sahib.