yes and no- towards the end of his life he did have several inventions, at least claimed he did, that he would only demonstrate for the right people- though these were generally reported to be weapons. He also had the resonator expiriment which shook, depending on accounts, either his entire building or a fair portion of a city block inNew York. but the biggest issue he would ave faced is money- Tesla had no understanding of finance and died in poverty, with only his drawings left. As such he would not have been able to stage a demonstration, and it is documented that the government did take his design documents upon his death (in fact there has been a long ranging political issue over whether those should belong to the US or his birth country- but this has focused primarilly o their historical value). So is it possible that some advanced design sits forgotten in a warehouse? Sure. The odds increase every year that we would have already designed something that meets or exceeds its specifications unless some of his wilder theories turned out to have paned out (in which case future generations might view it as something like the Roman steam engines which were designed but never built). But the most that can be done is to speculate on what might lie idden and forgotten, there is no need for conspiricy, but niether is there evidence that there is nothing. in fact given Tesla I would say there is an almost certainty that he designed more things that never saw the light of day, and some of them probably would have even worked.